A cake is removed from a 350◦F oven and placed on a cooling rack in a 70◦F room. After 30 minutes the cake is 200◦F. When will it be 100◦F?

Answers

Answer 1

Final answer:

The cake's temperature decreases according to Newton's Law of Cooling, and we can use this law to calculate the time it takes for the cake to reach a certain temperature.

Explanation:

The cake is removed from a 350°F oven and placed in a 70°F room. After 30 minutes, the cake's temperature decreases to 200°F. To find out when it will be 100°F, we can use Newton's Law of Cooling.

According to Newton's Law of Cooling, the rate of change of the temperature of an object is proportional to the difference between the object's temperature and the temperature of its surroundings. This can be expressed as:

T' = -k(T - Ts)

where T' is the rate of change of temperature with respect to time, T is the temperature of the object, Ts is the temperature of the surroundings, and k is the cooling constant. In this case, we can rearrange the equation to solve for time:

t = (1/k) * ln((T - Ts) / (T0 - Ts))

where t is the time, T0 is the initial temperature of the object, and ln is the natural logarithm.

Plugging in the values from the problem:

t = (1/k) * ln((200 - 70) / (350 - 70))

We can find the value of the cooling constant, k, by using the given information. Since we know the temperature dropped from 350°F to 200°F in 30 minutes, we can use this to find k:

-k = (T' / (T - Ts)) = (200 - 70) / (350 - 70) / 30

simplifying, we get:

k = -((200 - 70) / (350 - 70)) / 30

Now we can substitute the value of k into the equation for time:

t = (1 / -((200 - 70) / (350 - 70)))) * ln((200 - 70) / (350 - 70))

Calculating this equation will give us the approximate time it takes for the cake to reach 100°F.


Related Questions

Suppose you hear a clap of thunder 16.2 seconds after seeing the associated lightning stroke. The speed of sound waves in air is 343-m/s and the speed of light in air is 3.00 x 10^8-m/s. How far are you from the lightning stroke in both meters and miles? Assume that the light reaches you instantaneously.

Answers

Answer:

D = 3.45 mile

Explanation:

given,

time taken by the sound wave, t = 16.2 s

speed of sound, v = 343 m/s

speed of the light = 3 x 10⁸ m/s

distance where lightning stroke

 we know,

 distance = speed x time

  D = 343 x 16.2

  D = 5556.6 m

 1 m = 0.000621371 mile

5556.6 m = 5556.6 x 0.0006214

D = 3.45 mile

the distance lightning strike is 3.45 mile away from the observer.

Final answer:

To calculate the distance from a lightning stroke: use the time delay between seeing the lightning and hearing the thunder, and multiply it by the speed of sound (343 m/s). In this case, the lightning is approximately 5562.6 meters or about 3.46 miles away.

Explanation:

Your distance from a lightning stroke can be calculated by knowing the speed of sound and the time it takes for the sound from the lightning stroke to reach you. You said you hear the thunder sound 16.2 seconds after seeing the lightning. The speed of sound in air is 343 m/s. Therefore, the distance can be calculated using the formula: distance = speed * time.

In this case, distance = 343 m/s * 16.2s = 5562.6 meters or about 5.56 kilometers.

When this is converted to miles (since 1 mile is about 1609.34 meters), it is approximately 3.46 miles away. Therefore, based on the time difference between the flash and the thunder, you are about 5562.6 meters or 3.46 miles away from the lightning strike.

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The gravitational force exerted on a solid object is 5.00N. When the object is suspended from a spring scale and submerged completely in water the scale reads 3.50N. Find the density of the object.

Answers

Answer:

3333.33 kg/m³

Explanation:

Density: This can be defined as the ratio of the mass of a body to its volume.

The unit of density is kg/m³.

From Archimedes principle,

R.d = W/U = D/D'

Where R.d = relative density, W = weight of the object in air, u = upthrust in water, D = Density of the object, D' = Density of water.

W/U = D/D'

making D the subject of the equation

D = D'(W/U).......................... Equation 1

Given: W = 5.0 N, U = 5.0 -3.5 = 1.5 N, D' = 1000 kg/m³

Note: U = lost in weight = weight in air - weight in water

Substitute into equation 1

D = 1000(5/1.5)

D = 3333.33 kg/m³

Thus the density of the object = 3333.33 kg/m³

The first step is to calculate the buoyant force that the water exerts on the solid object. The buoyant force can be found by subtracting the scale reading from the gravitational force, or 5.00N - 3.50N = 1.50N.

Next, we find the volume of the water displaced by the solid. The buoyant force is equal to the weight of the fluid displaced, so we can use the formula F = ρf * V * g, where ρf is the fluid density, V is the water volume displaced, g is the acceleration due to gravity and F is the buoyant force.

We're given that the density of water is 9.8 * 1000 N/m³ and we've just calculated the buoyant force. Thus, we have 1.50N = 9.8 * 1000 * V * 9.81, which simplifies to V = 1.5 / (9.8 * 1000) = 0.0001530612244897959 m³.

Now we calculate the object's mass using the equation, m = F / g, where F is gravitational force and g is acceleration due to gravity. Substituting the given values, we get m = 5.00 / 9.81 = 0.509683995922528 kg.

Finally, we find the density of the object using the formula ρ = m / V, where m is the mass and V is the volume. Substituting the values calculated earlier, we get ρ = 0.509683995922528 / 0.0001530612244897959 = 3329.935440027183 kg/m³.

Therefore, the density of the object is approximately 3330 kg/m³.

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A 450g mass on a spring is oscillating at 1.2Hz. The totalenergy of the oscillation is 0.51J. What is the amplitude.

Answers

Answer:

A=0.199

Explanation:

We are given that  

Mass of spring=m=450 g=[tex]=\frac{450}{1000}=0.45 kg[/tex]

Where 1 kg=1000 g

Frequency of oscillation=[tex]\nu=1.2Hz[/tex]

Total energy of the oscillation=0.51 J

We have to find the amplitude of oscillations.

Energy of oscillator=[tex]E=\frac{1}{2}m\omega^2A^2[/tex]

Where [tex]\omega=2\pi\nu[/tex]=Angular frequency

A=Amplitude

[tex]\pi=\frac{22}{7}[/tex]

Using the formula

[tex]0.51=\frac{1}{2}\times 0.45(2\times \frac{22}{7}\times 1.2)^2A^2[/tex]

[tex]A^2=\frac{2\times 0.51}{0.45\times (2\times \frac{22}{7}\times 1.2)^2}=0.0398[/tex]

[tex]A=\sqrt{0.0398}=0.199[/tex]

Hence, the amplitude of oscillation=A=0.199

The amplitude of oscillation will be "0.199".

Given:

Mass of spring,

m = 450 g

or,

           = 0.45 kg

Frequency,

v = 1.2 Hz

Total energy,

E = 0.51 J

As we know the formula,

→ [tex]E = \frac{1}{2} m \omega^2 A^2[/tex]

By putting the values, we get

→ [tex]0.51= \frac{1}{2}\times 045 (2\times \frac{22}{7}\times 1.2 )^2 A^2[/tex]

→   [tex]A^2 = \frac{2\times 0.51}{0.45(2\times \frac{22}{7}\times 1.2 )^2}[/tex]

          [tex]= 0.0398[/tex]

→     [tex]A = \sqrt{0.0398}[/tex]

          [tex]= 0.199[/tex]

Thus the above response is right.

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Consider two waves X and Y traveling in the same medium. The two carry the same amount of energy per unit time, but X has one-seventh the amplitude of Y. What is the ratio of their wavelengths? (λY/λX=?)

Answers

Answer:

7 / 1

Explanation:

The ratio of their amplitude = one-seventh and the ratio of their amplitude = the ratio of their wavelength

Ax / Ay = λx / λy  = 1 / 7

λy / λx = 7 / 1

The ratio of wavelengths is λ(y)/λ(x) = 1/49.

The energy of a wave is directly proportional to the square of the amplitude of the wave.

   E ∝ [tex]A^{2}[/tex] , where E is the energy of the wave and A is the apmlitude

We also know that enegy

E = hc/λ

E ∝ 1/λ

According to the question:

Let wave X has energy [tex]E_x[/tex] and amplitude [tex]A_x[/tex]

and wave Y has energy [tex]E_y[/tex] and amplitude [tex]A_y[/tex]

[tex]\frac{E_x}{E_y}=\frac{A_x^2}{A_y^2} \\\\\frac{E_x}{E_y}= \frac{(A_y/7)^2}{A_y}\\\\\frac{E_x}{E_y}=\frac{1}{49}[/tex] since it is given that [tex]A_x=\frac{1}{7}A_y[/tex]

{1/λ(x)} / {1/λ(y)} = 1/49

λ(y)/λ(x) = 1/49 is the ratio of the wavelengths.

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The momentum of a type of bumper car at an amusement park should not exceed 2100 kg×m/s to ensure the safety of the visitors to the park. If each bumper car has a mass of 780 kg, will the ride be safe if the bumper cars are limited to a top speed of 3 m/s

Answers

Answer:

No, the ride will not be safe according to the standards mentioned in the question because the value of momentum exceeds.

Explanation:

Given:

magnitude of safe momentum of bumper cars, [tex]p=2100\ kg.m.s^{-1}[/tex]mass of each bumper car, [tex]m=780\ kg[/tex]top velocity of bumper car, [tex]v=3\ m.s^{-1}[/tex]

Now, we find the momentum of the car using the given mass and speed:

[tex]p'=m.v[/tex]

[tex]p'=780\times 3[/tex]

[tex]p'=2340\ kg.m.s^{-1}[/tex]

Therefore the ride will not be safe according to the standards mentioned in the question because the value of momentum exceeds.

Two radioactive nuclei A and B are present in equal numbers to begin with. Three days later, there are 4.04 times as many A nuclei as there are B nuclei. The half-life of species B is 1.37 days. Find the half-life of species A (in days).

Answers

Answer:

The half-life of A is 17.1 days.

Explanation:

Hi there!

The half-life of B is 1.73 days.

Let´s write the elapsed time (3 days) in terms of half-lives of B:

1.37 days = 1 half-life B

3 days = (3 days · 1 half-life B / 1.37 days) = 2.19 half-lives B.

After 3 days, the amount of A in terms of B is the following:

A = 4.04 B

The amount of B after 3 days can be expressed in terms of the initial amount of B (B0) and the number of half-lives (n):

B after n half-lives = B0 / 2ⁿ

Then after 2.19 half-lives:

B = B0 /2^(2.19)

In the same way, the amount of A can also be expressed in terms of the initial amount and the number of half-lives:

A = A0 / 2ⁿ

Replacing A and B in the equation:

A = 4.04 B

A0 / 2ⁿ = 4.04 · B0 / 2^(2.19)

Since A0 = B0

A0 / 2ⁿ = 4.04 · A0 / 2^(2.19)

Dividing by A0:

1/2ⁿ = 4.04 / 2^(2.19)

Multipliying by 2ⁿ and dividing by  4.04 / 2^(2.19):

2^(2.19) / 4.04 = 2ⁿ

Apply ln to both sides of the equation:

ln( 2^(2.19) / 4.04) = n ln(2)

n = ln( 2^(2.19) / 4.04) / ln(2)

n = 0.1756

Then, if 3 days is 0.1756 half-lives of A, 1 half-life of A will be:

1 half-life ·(3 days / 0.1756 half-lives) = 17.1 days

The half-life of A is 17.1 days.

If I time the movement of waves for 1 second, and calculate that 100 waves passed through in that 1 second, what have I calculated?

A.crest
B.amplitude
C.wavelength.
D.frequency.
E.none of the above

Answers

Answer:

D.frequency.

Explanation:

The number of times a wave passes through a particular point in a time of 1 second is called the frequency.

Amplitude is the maximum height the wave reaches from the reference axis of the wave

Wavelength is the distance between the two upper (crest) or lower (troughs) points of a wave.

Crest is the top most part of a wave.

Hence, the question is referring to frequency.

A can of soft drink at room temperature is put into the refrigerator so that it will cool. Would you model the can of soft drink as a closed system or as an open system?

Answers

Final answer:

The can of soft drink in a refrigerator is modelled as a closed system because while heat energy is exchanged with its surroundings, no matter is exchanged. An open system, in contrast, allows both energy and matter to be exchanged.

Explanation:

In the scenario where a can of soft drink is placed into a refrigerator to cool, you would model the can of soft drink as a closed system. A closed system is one in which energy can be exchanged with its surroundings, but matter cannot. In this case, the can of soft drink is transferring heat energy to its surroundings, i.e., the refrigerator, until equilibrium is achieved, but the soda itself remains within the can - no matter is exchanged.

An open system, on the other hand, allows both energy and matter to be exchanged with its environment. The dissolving of CO2 in soft drinks, as mentioned in the reference, is an example of an open system, where matter (CO2) is able to escape from the soft drink when the can or bottle is opened.

It's important to note that while practical real-world systems are ultimately open due to unavoidable interactions with the surroundings, we often model systems as closed (or even isolated) in order to simplify the analysis.

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The correct answer is that the can of soft drink would be modeled as a closed system.

In thermodynamics, a closed system is defined as a system that can exchange energy (such as heat) with its surroundings, but not matter. This means that while the can of soft drink can absorb or release heat to the refrigerator (its surroundings), no matter (like the soft drink itself) is exchanged between the can and the refrigerator.

Therefore, when the can of soft drink is placed in the refrigerator to cool, it is appropriately modeled as a closed system because only energy in the form of heat is transferred between the can and the refrigerator, and there is no transfer of matter.

The electric potential at a certain distance from a point charge can be represented by V. What is the value of the electric potential at twice the distance from the point charge?
The electric potential at a certain distance from a point charge can be represented by V. What is the value of the electric potential at twice the distance from the point charge?
At twice the distance, the electric potential is 4V.
At twice the distance, the electric potential is V/2.
At twice the distance, the electric potential is V/4.
At twice the distance, the electric potential is 2V.
At twice the distance, the electric potential remains V.

Answers

Answer:

At twice the distance, the electric potential is V/2.

Explanation:

The electric potential at a certain distance d from a point charge q can be represented by V:

V = kq/d .....1

Where q = charge ,d = distance between them, k = coulomb's constant.

When the distance is doubled d1 = 2d

Let V1 represent the electric potential after the distance have been doubled.

V1 = kq/2d = (kq/d)/2

V1 = V/2

Therefore, at twice the distance the electric potential is halved V1 = V/2

Final answer:

The electric potential (V) decreases as you increase your distance from the point charge. Therefore, at twice the distance from a charge, the electric potential will be halved, becoming V/2.

Explanation:

The electric potential (V) at a certain distance from a point charge, according to Coulomb's Law, is directly related to the charge and inversely related to the distance from it. Therefore, if we double the distance, the electric potential will be half as much. So, the electric potential at twice the distance from the point charge is V/2.

Think of it like this, if you're twice as far from the point charge, the effect of the charge (which in this case is represented by the electric potential) is lessened.

Therefore, the potential decreases as you increase your distance from the charge. Hence, at twice the distance from a charge, the electric potential will be halved, i.e., V/2.

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the equitorial diameter of the moon is 3476 kilometers. if a kilometer equals 0.6214 miles, what is the moon's diameter in miles?

Answers

To convert the equatorial diameter of the Moon from kilometers to miles, you can use the given conversion factor:

Equatorial diameter in miles = Equatorial diameter in kilometers × Conversion factor

Given:

Equatorial diameter of the Moon = 3476 kilometers

Conversion factor = 0.6214 miles/kilometer

Now, plug in the values:

Equatorial diameter in miles = 3476 km × 0.6214 miles/km

[tex]\[ \text{Equatorial diameter in miles} \approx 2160.9264 \, \text{miles} \][/tex]

So, the Moon's equatorial diameter is approximately 2160.93 miles.

Final answer:

To convert the Moon's diameter from 3476 kilometers to miles, multiply by the conversion factor of 0.6214 miles per kilometer, resulting in approximately 2160.6344 miles.

Explanation:

The question asks for the conversion of the Moon's diameter from kilometers to miles. The given diameter of the Moon is 3476 kilometers. To convert kilometers to miles, we use the provided conversion factor where 1 kilometer equals 0.6214 miles.

Here's how you can calculate the Moon's diameter in miles:

1. Multiply the Moon's diameter in kilometers by the conversion factor:
3476 kilometers × 0.6214 miles/kilometer

2. Calculating this gives:

2160.6344 miles
So, the Moon's diameter in miles is approximately 2160.6344.

If the plaque buildup (modeled as a cylinder as well) completely blocks the artery, a pressure difference of P between each side of the clot builds up. What is the force on the clot

Answers

Answer: Pπr2

Explanation: Force is any interaction that affects an object,that if not opposed or treated will cause some changes in the object. Pressure is directly proportional to force,which means an increase in force will create a corresponding increase in the pressure of a system.

The force on the cloth will be The PRESSURE EXERTED ON THE CLOT (P) *THE PI( which is the RATIO of the circumference of the cylinder i.e3.14159) *the square of the ratio. Which is Pπr2.

Final answer:

The force exerted on the artery clot can be determined by the formula F = P x A, where F is the force, P is the pressure and A is the area. In the case of a cylindrical clot, A = πr². Therefore, the force F = P x πr².

Explanation:

The force exerted on the clot by the pressure in the artery can be determined by using the formula for the force exerted by a pressure on a surface, which is Force (F)= pressure (P) x Area (A). The pressure is given as P. The area of the surface the pressure is exerted upon can be found by considering the cross-sectional area of the cylinder (clot), that can be expressed as the product of pi and the square of the radius (r), or πr².

Therefore, the force on the clot can be calculated by substituting the cross-sectional area (A = πr²) into the equation F = P x A, giving us F = P x πr². In this way, we can understand how the pressure in the artery results in a force on the clot.

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In an experiment, a shearwater (a seabird) was taken from its nest, flown a distance 5220 km away, and released. It found its way back to its nest 13.3 days after release.a) If we place the origin in the nest and extend the +x-axis to the release point, what was the bird's average velocity for the return flight? b)What was the bird's average velocity in m/s for the whole episode, from leaving the nest to returning?

Answers

Final answer:

For the return flight, the bird's average velocity is 6.38 m/s, while for the whole episode, the average velocity is 0 m/s.

Explanation:

a) To find the bird's average velocity for the return flight, we need to calculate the displacement and divide it by the time taken. The displacement is the distance between the release point and the nest, which is 5220 km. The time taken is 13.3 days, which can be converted to seconds by multiplying by 24 (hours in a day) and 60 (minutes in an hour). Therefore, the average velocity is:

Average velocity = displacement / time = 5220 km / (13.3 days * 24 hours/day * 60 minutes/hour * 60 seconds/minute) = 6.38 m/s

b) To find the bird's average velocity for the whole episode, we need to calculate the total displacement and divide it by the total time taken. The total displacement is 0 km, as the bird returns to its nest. The total time taken is the time taken for the return flight plus the time taken for the outward flight, which is 2 * 13.3 days. Therefore, the average velocity is:

Average velocity = total displacement / total time = 0 km / (2 * 13.3 days * 24 hours/day * 60 minutes/hour * 60 seconds/minute) = 0 m/s

If you were designing a room in a house, where would be the better place to put a heater, near the floor or near the ceiling? Why? Consider your answer in the context of convection.1. Near the ceiling, because the air warmed by the heater would quickly spread down and across the room, replacing the cold air.2. Near the floor, because the heater would warm the air close to it. After being heated, the now-warm air would rise, and be replaced by cool air, which the heater would warm. The cycle would continue until the room is heated.3. Near the ceiling, because the heater would warm the air close to it. After being heated, the now-warm air would descend, and be replaced by cool air, which the heater would warm. The cycle would continue until the room is heated.4. Near the floor, because the air warmed by the heater would quickly spread up and across the room, replacing the cold air.

Answers

Answer: The correct explanation is 2.

Explanation: The warm air is less dense (it expands) and thus it is lighter than the cold air so it will rise up to the floor. Therefore, when you place the heater on the floor it will warm the cold air which would then rise and be replaced by more cold air which would again get warm and rise and so on until the room is heated. This means that the correct explanation is 2.

On the other hand, if you put the heater at the ceiling, it will warm the cold air near the ceiling which would stay up there (it is lighter than the cold air under it). This means that the only way for the heat to spread from this ceiling level warm air to the lower levels is via conduction which is slow.  

Final answer:

The heater should be placed near the floor due to convection, where warm air rises after being heated, circulates, and evenly distributes throughout the room as it cools and descends. Therefore, option 2 is the correct answer.

Explanation:

Proper Placement of a Heater in a Room

When considering the placement of a heater in a room in the context of convection, the better option is to place the heater near the floor. This is because, as per the principles of convection, warm air will rise after being heated by the heater. The now-warm air, having become less dense, will rise to the ceiling, creating a convective loop that circulates the warm air throughout the room. As the air cools down near the ceiling and outside walls, it contracts, becoming denser, and subsequently sinks back to the floor, where it will be heated again by the heater. This cycle continues, leading to an efficient distribution of heat throughout the room. Therefore, option 2 is correct: placing the heater near the floor allows it to warm the air close to it, after which the warm air rises and is replaced by cool air that the heater warms again, maintaining a continuous cycle of heating.

A charge of + 3.00 μC is located at the origin, and a second charge of −2.00 μC is located on the x−y plane at the point (30.0 cm, 20.0 cm). Determine the electric force exerted by the −2.00 μC charge on the 3.00 μC charge.

Answers

Answer:

[tex]\vec{F} = -0.34\^x - 0.22\^y\\|\vec{F}| = -0.41~N[/tex]

Explanation:

The electric force between two point charges can be calculated by Coulomb's Law:

[tex]\vec{F} = \frac{1}{4\pi\epsilon_0}\frac{q_1q_2}{r^2}\^r[/tex]

We have to calculate the distance between two points; (0,0) and (0.3 m, 0.2 m).

[tex]r = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2} = \sqrt{(0.3)^2 + (0.2)^2} = 0.36~m[/tex]

Now we can apply Coulomb's Law

[tex]F = \frac{1}{4\pi\epsilon_0}\frac{(3\times 10^{-6})(-2\times 10^{-6})}{(0.36)^2} = -0.41~N[/tex]

The minus sign in front of the force means that the force is attractive.

The direction of the force can be calculated as follows:

[tex]F_x = F\cos(\theta)\\F_y = F\sin(\theta)[/tex]

where θ is the angle between F and the x-axis. This angle can be calculated by the triangle with edges 0.3 m, 0.2 m, and 0.36 m.  

So, sin(θ) = 0.2/0.36 = 0.55 and cos(θ) = 0.3/0.36 = 0.83.

Finally,

[tex]F_x = -0.41 \times 0.83 = -0.34~N\\F_y = -0.41 \times 0.55 = -0.22~N[/tex]

Final answer:

An electric force of approximately 0.0137 Newtons is exerted by the -2.00 μC charge on the 3.00 μC charge. The direction is attractive, implying that the force pulls the 3.00 μC charge towards the -2.00 μC charge.

Explanation:

The subject of this query pertains to the concept of electric force in Physics. Given the position coordinates and charge values, we can calculate the electric force between the two charges using Coulomb's Law, which states that the force between two charges is equal to the absolute value of the product of the charges, divided by the square of the distance between them, multiplied by the electrostatic constant (k = 8.99 x 10^9 N m²/C²).

First, determine the distance between the charges. Using the Pythagorean theorem, the distance is √(0.30² + 0.20²) = 0.36 m. Now plug the charge values (Q1=3.00 μC = 3.00 x 10^-6 C, Q2=-2.00 μC = -2.00 x 10^-6 C), and the distance (r=0.36 m) into Coulomb's Law (F=k|Q1*Q2|/r²).

The absolute value of the electric force would therefore be approximately |-2 x 8.99 x 10^9 N m²/C² x 3.00 x 10^-6 C x -2.00 x 10^-6 C / (0.36 m)²|, or about 0.0137 N (Newtons). Because force is a vector quantity, to find the direction of the force we need to consider the signs of the charges. Since they have opposite signs, the force is attractive, hence, the -2.00μC charge exerts a force towards itself on the +3.00 μC charge.

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At the instant when the electron is 4.40 cmcm from the wire and traveling with a speed of 6.10×104 m/sm/s directly toward the wire, what is the magnitude of the force that the magnetic field of the current exerts on the electron?

Answers

Answer:

The force that the magnetic field of the current exerts on the electron is [tex]2.30\times10^{-19}\ N[/tex]

Explanation:

Given that,

Distance = 4.40 cm

Speed [tex]v= 6.10\times10^{4}\ m/s[/tex]

Suppose a long, straight wire carries a current of 5.20 . An electron is traveling in the vicinity of the wire.

We need to calculate the magnetic field of the current exerts on the electron

Using formula of force

[tex]F=qv\times B[/tex]

[tex]F=qv\times\dfrac{\mu_{0}I}{2\pi r}[/tex]

Put the value into the formula

[tex]F=1.6\times10^{-19}\times6.10\times10^{4}\times\dfrac{4\pi\times10^{-7}\times5.20}{2\pi\times4.40\times10^{-2}}[/tex]

[tex]F=2.30\times10^{-19}\ N[/tex]

Hence, The force that the magnetic field of the current exerts on the electron is [tex]2.30\times10^{-19}\ N[/tex]

Calculate the period of a ball tied to a string of length 0.468 m making 3.8 revolutions every second. Answer in units of s. Your answer must be within ± 2.0%

Answers

Answer:

0.26315 s

Explanation:

The frequency of the ball tied to a string system is 3.8 rev/s.

That means in one second the ball will complete 3.8 revolutions.

The time period will be the reciprocal of this frequency

[tex]T=\dfrac{1}{f}\\\Rightarrow T=\dfrac{1}{3.8}\\\Rightarrow T=0.26315\ s[/tex]

The time period is 0.26315 s

It can be also solved in the following way

[tex]1\ s=3.8\ rev\\\Rightarrow 1\ rev=\dfrac{1}{3.8}\ s\\\Rightarrow 1\ rev=0.26315\ s[/tex]

The time period is 0.26315 s

Two identical conducting spheres, fixed in place, attract each other with an electrostatic force of -0.9537 N when separated by 50 cm, center-to-center. The spheres are then connected by a thin conducting wire. When the wire is removed, the spheres repel each other with an electrostatic force of 0.0756 N.
What were the initial charges on the spheres?

Answers

Answer:

The initial charges on the spheres are  [tex]6.796\ 10^{-6}\ c[/tex] and [tex]-3.898\ 10^{-6}\ c[/tex]

Explanation:

Electrostatic Force

Two charges q1 and q2 separated a distance d exert a force on each other which magnitude is computed by the known Coulomb's formula

[tex]\displaystyle F=\frac{K\ q_1\ q_2}{d^2}[/tex]

We are given the distance between two unknown charges d=50 cm = 0.5 m and the attractive force of -0.9537 N. This means both charges are opposite signs.

With these conditions we set the equation

[tex]\displaystyle F_1=\frac{K\ q_1\ q_2}{0.5^2}=-0.9537[/tex]

Rearranging

[tex]\displaystyle q_1\ q_2=\frac{-0.9537(0.5)^2}{k}[/tex]

Solving for q1.q2

[tex]\displaystyle q_1\ q_2=-2.6492.10^{-11}\ c^2\ \ ......[1][/tex]

The second part of the problem states the spheres are later connected by a conducting wire which is removed, and then, the spheres repel each other with an electrostatic force of 0.0756 N.

The conducting wire makes the charges on both spheres to balance, i.e. free electrons of the negative charge pass to the positive charge and they finally have the same charge:

[tex]\displaystyle q=\frac{q_1+q_2}{2}[/tex]

Using this second condition:

[tex]\displaystyle F_2=\frac{K\ q^2}{0.5^2}=\frac{K(q_1+q_2)^2}{(4)0.5^2}=0.0756[/tex]

[tex]\displaystyle q_1+q_2=2.8983\ 10^{-6}\ C[/tex]

Solving for q2

[tex]\displaystyle q_2=2.8983\ 10^{-6}\ C-q_1[/tex]

Replacing in [1]

[tex]\displaystyle q_1(2.8983\ 10^{-6}-q_1)=-2.64917.10^{-11}[/tex]

Rearranging, we have a second-degree equation for q1.  

[tex]\displaystyle q_1^2-2.8983.10^{-6}q_1-2.64917.10^{-11}=0[/tex]

Solving, we have two possible solutions

[tex]\displaystyle q_1=6,796.10^{-6}\ c[/tex]

[tex]\displaystyle q_1=-3.898.10^{-6}\ c[/tex]

Which yields to two solutions for q2

[tex]\displaystyle q_2=-3.898.10^{-6}\ c[/tex]

[tex]\displaystyle q_2=6.796.10^{-6}\ c[/tex]

Regardless of their order, the initial charges on the spheres are [tex]6.796\ 10^{-6}\ c[/tex] and [tex]-3.898\ 10^{-6}\ c[/tex]

Two car horns are sounded creating two sound waves with frequencies that differ by a factor of three. How does the speed of the higher frequency sound wave compare to the lower frequency sound wave?

Answers

Answer:

Remains the same

Explanation:

The speed of waves of higher and lower frequency both will be same.

the speed of sound in a medium is constant  and independent of it's frequency. Moreover, when the frequency changes wavelength changes accordingly, such that their product remains constant.

we know that

υ×λ = constant = velocity

υ= frequency

λ= wavelength.

If the momentum of a 1000 kg car travelling at 10 m/s was transferred completely to a 20.0 kg traffic barrier, what would the final speed of the barrier be
a. 40 m/s
b. 50 m/s
c. 250 m/s
d. 500 m/s

Answers

Answer:

d. 500 m/s

Explanation:

Momentum: This is the product of the mass of a body to its velocity, The S.I unit of momentum is kgm/s.

Mathematically, momentum can be expressed as,

M = mv....................... equation 1

Where M = momentum, m = mass, v = velocity

deduced from the question,

Momentum of the car = momentum of the barrier.

MV = mv ............................. Equation 1

Where M = mass of the car, V = velocity of the car, m = mass of the barrier, v = velocity of the barrier.

making v the subject of the equation,

v = MV/m........................ Equation 2

Given: M = 1000 kg, V = 10 m/s, m = 20 kg.

Substitute into equation 2

v = 1000(10)/20

v = 500 m/s.

Hence the speed of the barrier = 500 m/s

The right option is d. 500 m/s

A 3-in-thick slab is 12 in wide and 15 ft long. Thickness of the slab is reduced in three steps in a hot rolling operation. In each step, thickness is reduced by 20% and width increases by 3%. If the entry speed of the slab in the first step is 40 ft/min, and roll speed is the same for the three steps, determine (a) length and (b) exit velocity of the slab after the final reduction.

Answers

Answer:

[tex]L_f=26.8108 ft[/tex]

Part B:

For Final Reduction

[tex]v_f=48.5436ft/min[/tex]

Explanation:

Part A:

At each step 0.8 (100-20)% of thickness is left

Final Thickness t_f:

[tex]t_f=(0.80)(0.80)(0.80)*3\\t_f=1.536 in[/tex]

Width increases by 0.03 in each step so (100+3)%=1.03

Final Width w_f:

[tex]w_f=(1.03)(1.03)(1.03)*12\\w_f=13.1127 in[/tex]

Conservation of volume:

[tex]t_ow_oL_o=t_fw_fL_f\\L_f=\frac{t_ow_oL_o}{t_fw_f} \\L_f=\frac{3*12*(15*12)}{1.536*13.1127}\\L_f=321.730 in\\L_f=26.8108 ft[/tex]

Part B:

[tex]t_ow_ov_o=t_fw_fv_f[/tex]

At First reduction exit Velocity:

[tex]v_f=\frac{t_ow_oL_o}{t_fw_f} \\v_f=\frac{3*12*(40)}{0.8*3*1.03*12}\\v_f=48.5439ft/min[/tex]

At 2nd Reduction:

[tex]v_f=\frac{0.8*3*1.03*12*40}{0.8^2*3*1.03^2*12}\\v_f=48.5436ft/min[/tex]

For Final Reduction:

[tex]v_f=\frac{0.8^2*3*1.03^2*12*40}{0.8^3*3*1.03^3*12}\\v_f=48.5436ft/min[/tex]

Tamsen is interested in history, and read that because of its regular period, the pendulum constituted the basis of the most accurate clocks for nearly 300 years. Christian Huygens (1629-1695), the greatest clockmaker in history, suggested that an international unit of length could be defined as the length of a simple pendulum having a period of exactly 1 s.
Vera and Tamsen discuss how much shorter the SI unit of length, the meter, would have had to be had Huygens' suggestion been followed.
Which of their conclusions is correct?

a) 0.025 m b) 0.752 m c) 0.248 m d) 1.56 m

Answers

Final answer:

The correct conclusion would be 0.248 meters for the length of a pendulum with a period of 1 second. Therefore, the SI unit of length, the meter, would have had to be 0.752 m shorter had Huygens' suggestion to define it as the length of such a pendulum been followed.

Explanation:

The question proposes a discussion between Tamsen and Vera about how much shorter the SI unit of length, the meter, would have had to be if Christian Huygens' suggestion to define an international unit of length as the length of a simple pendulum with a period of 1 s, had been followed. Huygens' suggestion corresponds to the second pendulum or gravitational pendulum, which was an arrangement constituted by a simple pendulum adjusted so that its time of oscillation is exactly 2 seconds, meaning 'going and coming back'.

Mathematically, the formula to calculate the length of a pendulum with a given periodic time is given by L = g×(T/2×pi)² where g is the acceleration due to gravity and T is the period of the pendulum. For T = 1 second and g approximated to 9.81 m/s², the length derived would be approximately 0.248 meters. Therefore, among the given options, Vera and Tamsen's correct conclusion would be c) 0.248 m.

This means the SI unit of length, the meter, would have had to be 1 meter - 0.248 m = 0.752 m shorter had Huygens' suggestion been followed.

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During launches, rockets often discard unneeded parts. A certainrocket starts from rest on the launch pad and accelerates upward ata steady 3.25 m/s^2. When it is 230 m above the launch pad, it discards a usedfuel canister by simply disconnecting it. Once it is disconnected,the only force acting on the canister is gravity (air resistancecan be ignored).

A) How high is the rocket when thecanister hits the launch pad, assuming that the rocket does notchange its acceleration?
B) What total distance did the canistertravel between its release and its crash onto the launchpad?

Answers

Answer:

915.69549 m

306.1968 m

Explanation:

t = Time taken

u = Initial velocity

v = Final velocity

s = Displacement

a = Acceleration = 3.25 m/s²

g = Acceleration due to gravity = 9.81 m/s²

[tex]v^2-u^2=2as\\\Rightarrow v=\sqrt{2as+u^2}\\\Rightarrow v=\sqrt{2\times 3.25\times 230+0^2}\\\Rightarrow v=38.665\ m/s[/tex]

Height is given by

[tex]h=\dfrac{v^2}{2g}\\\Rightarrow h=\dfrac{38.665^2}{2\times 9.81}\\\Rightarrow h=76.1968\ m[/tex]

Total distance the canister has to travel is 230+76.1968 = 306.1968 m

Time to reach the max height

[tex]v=u+at\\\Rightarrow t=\dfrac{v-u}{g}\\\Rightarrow t=\dfrac{0-38.665}{-9.81}\\\Rightarrow t=3.9413\ s[/tex]

Time taken to reach the ground is

[tex]s=ut+\frac{1}{2}gt^2\\\Rightarrow 306.1968=0t+\frac{1}{2}\times 9.81\times t^2\\\Rightarrow t=\sqrt{\frac{306.1968\times 2}{9.81}}\\\Rightarrow t=7.9\ s[/tex]

Total time taken would be 3.9413+7.9 = 11.8413 seconds

[tex]s=ut+\dfrac{1}{2}at^2\\\Rightarrow s=38.665\times 11.8413+\dfrac{1}{2}\times 3.25\times 11.8413^2\\\Rightarrow s=685.69549\ m[/tex]

The rocket is 685.69549+230 = 915.69549 m from the launchpad.

The total distance is 230+76.1968 = 306.1968 m

The unit weight of a soil is 96 lb/ft3 . The moisture content if this soil is 17% when the degree of saturation is 60%. Determine: a. Void ratio b. Specific gravity of solids c. Saturated unit weight.

Answers

Final answer:

The void ratio of the soil is 1.2045, the specific gravity of solids is 2.6329, and the saturated unit weight is 82.7586 lb/ft3.

Explanation:

The void ratio of the soil can be determined using the formula:

e = (1 + w) / (1 - w)

where e is the void ratio and w is the moisture content. Plugging in the values, we get:

e = (1 + 0.17) / (1 - 0.17) = 1.2045

To calculate the specific gravity of solids, we can use the formula:

Gs = (1 + e) * (1 - S) / (1 - e * S)

where Gs is the specific gravity of solids and S is the degree of saturation. Substituting the given values:

Gs = (1 + 1.2045) * (1 - 0.6) / (1 - 1.2045 * 0.6) = 2.6329

The saturated unit weight can be found using the equation:

Gamma_sat = Gamma_dry / (1 + w)

where Gamma_sat is the saturated unit weight and Gamma_dry is the dry unit weight. Given that the unit weight of the soil is 96 lb/ft3, we have:

Gamma_sat = 96 / (1 + 0.17) = 82.7586 lb/ft3

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A piece of tape is pulled from a spool and lowered toward a 190-mg scrap of paper. Only when the tape comes within 8.0 mm is the electric force magnitude great enough to overcome the gravitational force exerted by Earth on the scrap and lift it.
Determine the magnitude and direction of the electric force exerted by the tape on the paper at this distance

Answers

Final answer:

The magnitude of the electric force exerted by the tape on the paper at a distance of 8.0 mm is 3.72 x 10^-7 C. The direction of the force is repulsive as like charges repel each other.

Explanation:

When the tape comes within 8.0 mm of the scrap of paper, the electric force magnitude is great enough to overcome the gravitational force exerted by Earth on the scrap and lift it. To determine the magnitude and direction of the electric force exerted by the tape on the paper at this distance, we can use the equation for the electric force:

F = k * (Q1 * Q2) / r^2

where F is the magnitude of the force, k is the Coulomb's constant (8.99 x 10^9 Nm^2/C^2), Q1 and Q2 are the charges, and r is the distance between the charges.

We know that the gravitational force is equal to the weight of the paper:

Fg = m * g

where Fg is the gravitational force, m is the mass of the paper (190 mg = 0.190 g), and g is the acceleration due to gravity (9.8 m/s^2).

At the point where the tape comes within 8.0 mm of the paper, the electric force is equal to the gravitational force:

F = Fg

k * (Q1 * Q2) / r^2 = m * g

We can solve this equation for the magnitude of the charge Q1 or Q2:

Q1 * Q2 = (m * g * r^2) / k

Substituting the known values, we get:

Q1 * Q2 = (0.190 g * 9.8 m/s^2 * (8.0 mm)^2) / (8.99 x 10^9 Nm^2/C^2)

Q1 * Q2 = 1.383 x 10^-12 C^2

To find the magnitude of the charge, we can assume that Q1 and Q2 are equal, so:

Q1 = Q2 = sqrt(1.383 x 10^-12 C^2) = 3.72 x 10^-7 C

The magnitude of the electric force exerted by the tape on the paper at this distance is 3.72 x 10^-7 C. The direction of the force is repulsive because like charges repel each other.

The bellow of a territorial bull hippopotamus is measured at 106 dB above the threshold of hearing. What is the sound intensity? Hint: The threshold of human hearing is I0 = 1.00 x 10-12 W/m2.

Answers

Answer:

0.03981 W/m²

Explanation:

I = Sound intensity

[tex]\beta[/tex] = Intensity level = 106 dB

[tex]I_0[/tex] = Threshold of human hearing = [tex]10^{-12}\ W/m^2[/tex]

Intensity of sound is given by

[tex]\beta=10log\dfrac{I}{I_0}\\\Rightarrow 106=10log\dfrac{I}{10^{-12}}\\\Rightarrow \dfrac{106}{10}=log\dfrac{I}{10^{-12}}\\\Rightarrow 10^{\dfrac{106}{10}}=\dfrac{I}{10^{-12}}\\\Rightarrow I=10^{\dfrac{106}{10}}\times 10^{-12}\\\Rightarrow I=10^{-1.4}\\\Rightarrow I=0.03981\ W/m^2[/tex]

The sound intensity is 0.03981 W/m²

Final answer:

The sound intensity is approximately 1.00 x 10^-4 W/m^2.

Explanation:

The sound intensity can be calculated using the formula:

I = I0 * 10^(dB/10)

where I is the sound intensity, I0 is the threshold of human hearing (given as 1.00 x 10^-12 W/m^2), and dB is the decibel level above the threshold. In this case, the decibel level is 106 dB. Plugging in the given values into the formula:

I = (1.00 x 10^-12 W/m^2) * 10^(106/10)

Simplifying the equation:

I ≈ 1.00 x 10^-4 W/m^2

The sound intensity is approximately 1.00 x 10^-4 W/m^2.

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A positron is an elementary particle identical to an electron except that its charge is . An electron and a positron can rotate about their center of mass as if they were a dumbbell connected by a massless rod.What is the orbital frequency for an electron and a positron 1.50 apart?

Answers

Explanation:

According to the energy conservation,

          [tex]F_{centripetal} = F_{electric}[/tex]

            [tex]\frac{mv^{2}}{r} = \frac{kq^{2}}{d^{2}}[/tex]

           [tex]v^{2} = \frac{kq^{2}r}{d^{2}m}[/tex]

                 = [tex]\frac{9 \times 10^{9} N.m^{2}/C^{2} \times 1.6 \times 10^{-19} C \times 0.75 \times 10^{-9} m}{(1.50 \times 10^{-9}m)^{2} \times 9.11 \times 10^{-31} kg}[/tex]

                = [tex]8.430 \times 10^{10} m^{2}/s^{2}[/tex]

             v = [tex]\sqrt{8.430 \times 10^{10} m^{2}/s^{2}}[/tex]

                = [tex]2.903 \times 10^{5} m/s[/tex]

Formula for distance from the orbit is as follows.

               S = [tex]2 \pi r[/tex]

                  = [tex]2 \times 3.14 \times 0.75 \times 10^{-9} m[/tex]

                  = [tex]4.71 \times 10^{-9} m[/tex]

Now, relation between time and distance is as follows.

                T = [tex]\frac{S}{v}[/tex]

       [tex]\frac{1}{f} = \frac{S}{v}[/tex]

or,           f = [tex]\frac{v}{S}[/tex]          

                = [tex]\frac{2.903 \times 10^{5} m/s}{4.71 \times 10^{-9} m}[/tex]      

                = [tex]6.164 \times 10^{13} Hz[/tex]

Thus, we can conclude that the orbital frequency for an electron and a positron that is 1.50 apart is [tex]6.164 \times 10^{13} Hz[/tex].

Using simple rearrangement of Newton's second law, show that a net force of 77 N exerted on a 11-kg package is needed to produce an acceleration of 7.0 m/s2 .

Answers

Answer:

A net force of 11 kg is needed to produce an acceleration of 7.0 m/s²

Explanation:

Newton's Second Law: It states that the the rate of change of momentum of a body, is directly proportional to the applied force, and takes place along the direction of the the force.

From Newton's second law of motion, we can deduced that,

F = ma ......................... Equation 1.

Where F = Net force acting on the package, m = mass of the package, a = acceleration of the page.

From the question, when

F = 77 N, m = 11 kg.

a = F/m

a = 77/11

a = 7 m/s².

From the above, a net force of 11 kg is needed to produce an acceleration of 7.0 m/s²

Final answer:

To determine the net force needed to accelerate an 11-kg package at 7.0 m/s², apply Newton's second law using the formula Fnet = ma, which yields a net force of 77 N.

Explanation:

The student is asking how to use Newton's second law to calculate the net force required to produce a certain acceleration for an object of known mass. This is a physics problem that involves using the formula Fnet = ma (where Fnet is the net force, m is the mass, and a is the acceleration).

In this case, the mass m of the package is 11 kg, and the desired acceleration a is 7.0 m/s². To find the net force Fnet, we rearrange the formula as it is already in the form solving for the net force and simply substitute the known values:

Fnet = (11 kg) × (7.0 m/s²)

Now, we multiply:

Fnet = 77 N

Therefore, a net force of 77 N is indeed needed to accelerate an 11-kg package at 7.0 m/s².

In very cold weather, a significant mechanism for heat loss by the human body is energy expended in warming the air taken into the lungs with each breath. A) On a cold winter day when the temperature is -19.0 C, what is the amount of heat needed to warm to internal body temperature (37 C ) the 0.470 J (Kg *K) of air exchanged with each breath? Assume that the specific heat capacity of air is 1020 and that 1.0 L of air has a mass of 1.3 g . B) How much heat is lost per hour if the respiration rate is 21.0 breaths per minute?

Answers

Final answer:

To warm the cold air inhaled during a breath to body temperature requires about 35.05J of energy or heat. This results in a total loss of around 44.16 KJ of heat due to respiration per hour.

Explanation:

This is a question about the heat exchange between the human body and the surrounding air when breathing, in cold weather conditions. We can solve it using the concepts of heat transfer and specific heat capacity.

A. To find the amount of heat necessary to warm the cold air to body temperature, we first need to determine the change in temperature. This would be (37-(-19)) = 56°C. The mass of the air breathed in with each breath can be calculated as 0.470L * 1.3g/L = 0.611g. Converting this to kg, we get 0.000611 Kg. The quantity of heat, Q, can be found using the formula Q = mcΔT, where m is the mass, c is the specific heat capacity, and ΔT is the change in temperature. Plugging in the values, we get Q = 0.000611 Kg * 1020 J/Kg°C * 56°C = 35.05J.

B. The total amount of heat lost per hour due to respiration can be calculated by first finding the heat lost per minute: Q per minute = Q per breath * respiration rate = 35.05J/breath * 21 breaths/minute = 736.05 J/minute. Converting this to an hourly rate gives us 736.05 J/minute * 60 minutes/hour = 44,163J/hour or about 44.16 KJ/hour. So, about 44.16 KJ of heat is lost via respiration each hour.

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Final answer:

The amount of heat needed to warm to internal body temperature the air exchanged with each breath on a cold day is 74.3 J per breath. The total heat loss per hour for a respiration rate of 21.0 breaths per minute is approximately 93.6 kJ/hour.

Explanation:

To calculate the amount of heat needed to warm the air inhaled during breathing to the internal body temperature, we can use the formula:

Q = mcΔT

Where:

Q is the heat energy (in joules),m is the mass of air (in kilograms),c is the specific heat capacity of air (in J/kg·K),ΔT is the change in temperature (in Kelvin).

The mass of 1.0 L of air at 1.3 g/L is 0.0013 kg. The change in temperature needed to warm air from -19°C to 37°C is 56°C or 56 K since the size of 1 degree on both scales is the same. Thus:

Q = 0.0013 kg * 1020 J/kg·K * 56 K

Q = 74.3 J per breath.

To find the heat lost per hour at a respiration rate of 21.0 breaths per minute, we do:

Heat loss per hour = Q * number of breaths per hour = 74.3 J * (21 breaths/min * 60 min/hour)

Heat loss per hour = 74.3 J * 1260 breaths/hour = 93618 J/hour, or approximately 93.6 kJ/hour.

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A bullet of mass 0.01 kg moving horizontally strikes a block of wood of mass 1.5 kg which is suspended as a pendulum. The bullet lodges in the wood, and together they swing upwards a distance of 0.40 m. What was the velocity of the bullet just before it struck the wooden block

Answers

Answer:

423m/s

Explanation:

Suppose after the impact, the bullet-block system swings upward a vertical distance of 0.4 m. That's means their kinetic energy is converted to potential energy:

[tex]E_p = E_k[/tex]

[tex]mgh = mv^2/2[/tex]

where m is the total mass and h is the vertical distance traveled, v is the velocity right after the impact at, which we can solve by divide both sides my m

Let g = 9.81 m/s2

[tex]gh = v^2/2[/tex]

[tex]v^2 = 2gh = 2 * 9.81* 0.4 = 7.848[/tex]

[tex]v = \sqrt{7.848} = 2.8m/s[/tex]

According the law of momentum conservation, momentum before and after the impact must be the same

[tex]m_uv_u + m_ov_o = (m_u + m_o)v[/tex]

where [tex]m_u = 0.01, v_u[/tex] are the mass and velocity of the bullet before the impact, respectively.[tex]m_ov_o[/tex] are the mass and velocity of the block before the impact, respectively, which is 0 because the block was stationary before the impact

[tex]0.01v_u + 0 = (0.01 + 1.5)*2.8[/tex]

[tex]0.01v_u = 4.23[/tex]

[tex]v_u = 4.23 / 0.01 = 423 m/s[/tex]

The initial velocity of the bullet just before it struck the block was 422 m/s.


To determine the velocity of a bullet just before it strikes a block of wood and causes a ballistic pendulum motion, we follow these steps:

First, identify the masses: the bullet (0.01 kg) and the wooden block (1.5 kg). Together, they have a combined mass of (1.51 kg) after the bullet lodges in the wood.Next, use the height they rise to find the velocity after collision. The potential energy at the highest point (0.40 m) is converted from kinetic energy:
PE = KE
mgh = 0.5m[tex]v^{2}[/tex]
where g is the acceleration due to gravity (9.8 m/s²), h is height (0.40m), and m is the total mass.Plug in the values:
(1.51 kg)(9.8 m/s²)(0.4 m) = 0.5(1.51 kg)[tex]v^{2}[/tex]
Solving this gives:5.912 J = 0.755[tex]v^{2}[/tex]
V² = 7.828
V = 2.8 m/sNow use the conservation of momentum to find the initial velocity of the bullet. Initially, only the bullet has momentum:

[tex]p_{initial}[/tex] = [tex]P_{final}[/tex]
(0.01 kg)u = (1.51 kg)(2.8 m/s)
Simplifying this:
u = 1.51 kg * 2.8 m/s / 0.01 kg
u = 422 m/s

Thus, the initial velocity of the bullet just before it struck the block was 422 m/s.

A 0.10 kg meter stick is held perpendicular to a vertical wall by a 2.5 mm string going from the wall to the far end of the stick.
(A) Find the tension in the string.
(B) If a shorter string is used, will its tension be greater than, less than, or the same as that found in part (A)?
(C) Find the tension in a 2.0 m string.

Answers

Explanation:

a)

Sum of moments = 0 (Equilibrium)

T . cos (Q)*L = m*g*L/2

[tex]cos Q = \frac{\sqrt{(2.5^2 - L^2) } }{2.5}[/tex]

[tex]T*\frac{\sqrt{(2.5^2 - L^2) } }{2.5} * L = 0.1 *9.81*L/2[/tex]

[tex]T = \frac{2.4525}{\sqrt{(2.5)^2 - L^2} }[/tex]

b) If the String is shorter the Q increases; hence, Cos Q decreases which in turn increases Tension in the string due to inverse relationship!

c)

[tex]T = \frac{1.962}{\sqrt{(2)^2 - L^2} }[/tex]

The rotational equilibrium condition allows finding the responses for the tension of the rope are:

   A) T = 0.53 N

   B) If the rope shortens the tension increase..

   C) T = 0.57 N

Newton's second law for rotational motion gives a relationship between the torque, the moment of inertia and the angular acceleration of the bodies, in the special case that the acceleration is zero, it is called the equilibrium condition.

                 

                  Σ τ = 0

Torque is defined as the vector product of the force and the distance, its modulus is:

                τ = F rsin θ  

where τ is the torque, F the force, r the distance and tea the angle between the force and the distance, it is a product (r sin θ ) it is called the perpendicular distance or arm.

In the attached we have a free body diagram of the system, let's apply the equilibrium condition,

Let's use trigonometry to descompose the force.  

                cos θ = [tex]\frac{T_x}{T}[/tex]  

               sin  θ = [tex]\frac{T_y}{T}[/tex]  

               Tₓ = T cos θ

               [tex]T_y[/tex] = T sin  θ

They indicate that the length of the bar is x = 1 m and the length of the cable is L = 2.5 m, let's find the angle

             cos  θ = [tex]\frac{x}{L}[/tex]  

              θ = cos⁻¹ [tex]\frac{x}{L}[/tex]  

              θ = cos⁻¹ [tex]\frac{1}{2.5}[/tex]

              θ = 66.4º

A) let's set our pivot point at the junction with the wall and the anti-clockwise direction of rotation is positive.

                 W [tex]\frac{L}{2}[/tex]  - Ty L = 0

                 W [tex]\frac{L}{2}[/tex]  = (T sin 66.4) L

                 [tex]T = \frac{mg}{s sin 66.4} \\ \\T = \frac{0.1 \ 9.8}{2 \ sin66.4}[/tex]  

                 T = 0.53 N

B) how the tension changes as the length of the string changes.

               T = [tex]\frac{mg}{2 sin \theta}[/tex]  

we can see that the change of the tension occurs by changing the value of the sine function.

           sin θ = [tex]\frac{y}{L_o}[/tex]

Let's use the Pythagorean theorem to find the opposite leg.

         L² = x² + y²

         y = [tex]\sqrt{L^2 - x^2 }[/tex] = [tex]L \ \sqrt {1^2 + (\frac{x}{L})^2 }[/tex]

Let's substitute.

         sin θ =  [tex]\sqrt{1 - \frac{x^2}{L^2} }[/tex]

if we use a binomial expansion.

          [tex](1 - a) ^{0.5} = 1 - \frac{1}{2} a + ...[/tex]

Let's substitute.

            sin  θ  = 1 -  [tex]\frac{1}{2} \ \frac{x}{L}[/tex]    

We can see that when the value of the length decreases the value of the sine decreases and this term is in the denominator of the expression of the tension, therefore the tension must increase.

C) the length of the rope is L = 2 m

           sin θ =  [tex]\sqrt{1 - (\frac{1}{2})^2 }[/tex]  

           sin θ = 0.866

           T = [tex]\frac{mg}{2sin \theta}[/tex]  

            T = [tex]\frac{0.1 \ 9.8}{2 \ 0.866}[/tex]  

            T =0.57 N

In conclusion, using the rotational equilibrium condition we can find the answers for the tension of the rope are:

   A) T = 0.53 N

   B) If the rope shortens the tension increase.

   C) T = 0.57 N

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