# Quiz: Work, Power And Energy

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Practice quiz for chapter 7.

• 1.

### A solar collector heats the water in the water tank of a home. Which energy transformation equation best describes this situation?

• A.

• B.

• C.

• D.

• E.

Explanation
In this situation, the solar collector absorbs radiant energy from the sun and converts it into thermal energy. The thermal energy is then used to heat the water in the water tank. Therefore, the energy transformation equation that best describes this situation is "radiant --> thermal".

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• 2.

### The amount of work done when a 80.00-kg person jumps 1.000 m into the air in 0.5000 s is

• A.

292.0 J

• B.

40.00 J

• C.

784.00 J

• D.

1568 J

• E.

160.0 J

C. 784.00 J
Explanation
When a person jumps into the air, work is done against gravity. The work done is equal to the force applied multiplied by the distance moved in the direction of the force. In this case, the force is the weight of the person, which is equal to their mass multiplied by the acceleration due to gravity. The distance moved is the height the person jumps, which is given as 1.000 m. The work done is calculated by multiplying the force by the distance, resulting in 784.00 J.

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• 3.

### The amount of work done to stop a bullet travelling through a tree trunk a distance of 50 cm with a force of 2.00 Â´ 102 N is

• A.

â€“4.00 x 102 J

• B.

+4.00 x 102 J

• C.

+1.00 x 102 J

• D.

â€“1.00 x 102 J

• E.

+1.00 x 104 J

D. â€“1.00 x 102 J
Explanation
The negative sign in the answer indicates that work is done against the force of the bullet, which is in the opposite direction of the displacement. The magnitude of the work done is 1.00 x 102 J, indicating that 100 Joules of work is done to stop the bullet from travelling through the tree trunk.

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• 4.

### A person lifts a pail of water of mass of 1.50 kg from the ground to a deck, 1.00 m above the ground. How much work was done by gravitational force on the pail of water?

• A.

â€“14.7 J

• B.

+1.50 J

• C.

â€“1.50 J

• D.

+0.153 J

• E.

+14.7 J

A. â€“14.7 J
Explanation
The negative sign in the answer indicates that the work done by the gravitational force is in the opposite direction of the displacement. Since the pail is lifted upwards, the displacement is in the positive direction. However, the gravitational force acts downwards, so the work done by it is negative. The magnitude of the work done can be calculated using the formula W = mgh, where m is the mass of the pail, g is the acceleration due to gravity, and h is the height. Plugging in the given values, we get W = (1.5 kg)(9.8 m/s^2)(1.0 m) = -14.7 J. Therefore, the correct answer is -14.7 J.

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• 5.

### In which case is negative work done?

• A.

The work done by Earth on a ball as the ball, which was initially at rest, falls 3.0 m down towards Earth.

• B.

A eastward force is applied to an eastward moving soccer ball that is already moving at a constant velocity to increase its speed in that direction.

• C.

A cart is moving at a constant velocity of 10 m/s [W] when a 0.5 N [downward] force is applied.

• D.

The work done by Earth on an arrow as it is fired 200 m straight up into the air.

• E.

Earth applies a force on the Moon as the Moon travels one completion rotation in orbit around Earth.

D. The work done by Earth on an arrow as it is fired 200 m straight up into the air.
• 6.

### In which case is positive work done?

• A.

The work done by air resistance on a ball as the ball, which was initially at rest, falls 3.0 m down towards Earth.

• B.

A eastward force is applied to an eastward moving soccer ball that is already moving at a constant velocity to increase its speed in that direction.

• C.

Earth applies a force on the Moon as the Moon travels one completion rotation in orbit around Earth.

• D.

A cart is moving at a constant velocity of 10 m/s [W] when a 0.5 N [downward] force is applied.

• E.

The work done by Earth on an arrow as it is fired 200 m straight up into the air.

B. A eastward force is applied to an eastward moving soccer ball that is already moving at a constant velocity to increase its speed in that direction.
Explanation
When a force is applied to an object in the same direction as its motion, positive work is done. In this case, the eastward force is applied to an eastward moving soccer ball, which means the force and the displacement are in the same direction. As a result, positive work is done on the ball, increasing its speed in the eastward direction.

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• 7.

### An elevator motor lifts a load of 2500 kg a height of 12.0 m in 3.00 seconds. The energy required by the motor to accomplish this task is 300 000 J. What is the efficiency of the elevator?

• A.

10.0%

• B.

98.0%

• C.

30.0%

• D.

102%

• E.

8.17%

B. 98.0%
Explanation
The efficiency of a machine is defined as the ratio of output work to input work, expressed as a percentage. In this case, the output work is the energy required to lift the load (300,000 J), and the input work is the energy supplied to the motor. Since the motor is lifting the load against gravity, the input work is equal to the gravitational potential energy gained by the load, which is given by mgh, where m is the mass (2500 kg), g is the acceleration due to gravity (9.8 m/s^2), and h is the height (12.0 m). Therefore, the input work is 2500 kg * 9.8 m/s^2 * 12.0 m = 294,000 J. The efficiency is then calculated as (output work / input work) * 100% = (300,000 J / 294,000 J) * 100% â‰ˆ 102%. However, since efficiency cannot exceed 100%, the correct answer is 98.0%.

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• 8.

### In the following figure, a 0.60-kg ball is about to fall to the step below.  The gravitational potential energy of the ball relative to the step is

• A.

8.8 x 101 J

• B.

2.9 x 101 J

• C.

6.0 x 100 J

• D.

3.0 x 100 J

• E.

5.9 x 101 J

E. 5.9 x 101 J
• 9.

### Jughead (m = 60 kg), Archie (m = 65 kg), and Reggie (m = 70 kg), all decide to run up a flight of stairs at with a height of 4.0 m at constant speed at good olâ€™ Riverdale High.  If all three achieve this task in a time of 3.5 seconds, who generates the most power?

• A.

• B.

Archie

• C.

Reggie

• D.

They all generate the same amount of power

• E.

Not enough information is provided to answer this question

C. Reggie
Explanation
Reggie generates the most power because power is calculated by dividing work by time, and work is equal to force multiplied by distance. Since all three achieve the task in the same time, the one with the highest mass (Reggie) would exert the most force while climbing the stairs. Therefore, Reggie generates the most power.

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• 10.

### During a recent NBA basketball game, Jose Calderon, a guard with the Toronto Raptors, threw a basketball into the crowd in an unsportsmanlike manner.  Which one of the following statements about the basketball is FALSE?

• A.

As the basketball rises, its kinetic energy decreases

• B.

As the basketball rises, it is accelerated downward

• C.

As the basketball rises, its potential energy increases

• D.

When the basketball reaches the top of its flight, its kinetic energy is zero

• E.

When the basketball reaches the top of its flight, acceleration is still g

D. When the basketball reaches the top of its flight, its kinetic energy is zero
Explanation
When the basketball reaches the top of its flight, its kinetic energy is zero. As the basketball rises, its potential energy increases due to its position in the gravitational field. As the basketball rises, it is accelerated downward due to the force of gravity. However, at the top of its flight, the basketball momentarily comes to a stop before descending. At this point, its velocity is zero, resulting in zero kinetic energy.

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• 11.

### Nicholas exerts a certain force to lift a dumbell 3.0 m straight above his head in 20 s. If he had completed the same task in 10 s, the energy he would need to use would be

• A.

Twice as great

• B.

The same

• C.

Four times as great

• D.

Half as great

• E.

Cannot be calculated using the given information

B. The same
Explanation
If Nicholas exerts a certain force to lift the dumbbell 3.0 m above his head in 20 s, it means he is using a certain amount of energy to perform the task. If he completes the same task in half the time, 10 s, it implies that he is exerting the same force but for a shorter duration. Since the force applied remains the same, the energy used would also be the same.

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• 12.

### If Elio pushes against an immobile wall with twice as much force as Jordan, which of the following is TRUE?

• A.

Elio is doing twice as much work as Jordan.

• B.

Elio generates twice as much power as Jordan.

• C.

Elio is doing four times as much work as Jordan.

• D.

No work is being done by Elio or Jordan.

• E.

They both generate power in equal amounts.