Energize Your Knowledge: Work, Power, and Energy Quiz

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

Radiant --> thermal

Radiant --> electrical

Radiant --> gravitational --> electrical

Radiant --> gravitational --> thermal

Radiant --> thermal --> electrical

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

Explanation

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

2. 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 ol’ Riverdale High. If all three achieve this task in a time of 3.5 seconds, who generates the most power?

Jughead

Archie

Reggie

They all generate the same amount of power

Not enough information is provided to answer this question

Reggie generates the most power because power is calculated as work done divided by time, and work done is equal to force multiplied by distance. Since all three individuals run up the same flight of stairs at the same constant speed, the work done is the same for each of them. However, power is inversely proportional to time, so the individual who completes the task in the shortest amount of time generates the most power. Since Reggie, who weighs the most, completes the task in the same time as the others, he generates the most power.

Explanation

Reggie generates the most power because power is calculated as work done divided by time, and work done is equal to force multiplied by distance. Since all three individuals run up the same flight of stairs at the same constant speed, the work done is the same for each of them. However, power is inversely proportional to time, so the individual who completes the task in the shortest amount of time generates the most power. Since Reggie, who weighs the most, completes the task in the same time as the others, he generates the most power.

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

292.0 J

40.00 J

784.00 J

1568 J

160.0 J

When a person jumps into the air, work is done against gravity. The work done can be calculated using the formula: work = force x distance. In this case, the force is the weight of the person, which can be calculated as mass x gravity. The distance is the height jumped. Therefore, the work done is equal to (80.00 kg x 9.8 m/s^2) x 1.000 m = 784.00 J.

Explanation

When a person jumps into the air, work is done against gravity. The work done can be calculated using the formula: work = force x distance. In this case, the force is the weight of the person, which can be calculated as mass x gravity. The distance is the height jumped. Therefore, the work done is equal to (80.00 kg x 9.8 m/s^2) x 1.000 m = 784.00 J.

4. 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?

10.0%

98.0%

30.0%

102%

8.17%

The efficiency of a system is calculated by dividing the useful output energy by the total input energy and multiplying by 100%. In this case, the useful output energy is the work done by the elevator motor to lift the load, which is equal to the weight of the load multiplied by the height it is lifted. The total input energy is given as 300,000 J. Therefore, the efficiency can be calculated as (useful output energy / total input energy) * 100%. The efficiency is 98.0%.

Explanation

The efficiency of a system is calculated by dividing the useful output energy by the total input energy and multiplying by 100%. In this case, the useful output energy is the work done by the elevator motor to lift the load, which is equal to the weight of the load multiplied by the height it is lifted. The total input energy is given as 300,000 J. Therefore, the efficiency can be calculated as (useful output energy / total input energy) * 100%. The efficiency is 98.0%.

5. In which case is positive work done?

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

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.

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

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

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

In this case, positive work is done because the force applied is in the same direction as the displacement of the ball. According to the work-energy principle, work is defined as the dot product of force and displacement. When the force and displacement are in the same direction, the angle between them is 0 degrees, resulting in positive work.

Explanation

In this case, positive work is done because the force applied is in the same direction as the displacement of the ball. According to the work-energy principle, work is defined as the dot product of force and displacement. When the force and displacement are in the same direction, the angle between them is 0 degrees, resulting in positive work.

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

Elio is doing twice as much work as Jordan.

Elio generates twice as much power as Jordan.

Elio is doing four times as much work as Jordan.

No work is being done by Elio or Jordan.

They both generate power in equal amounts.

If Elio pushes against an immobile wall, no work is being done because work is defined as the product of force and displacement. Since the wall is immobile, there is no displacement and therefore no work is being done by Elio. The same applies to Jordan as well. Therefore, no work is being done by either Elio or Jordan.

Explanation

If Elio pushes against an immobile wall, no work is being done because work is defined as the product of force and displacement. Since the wall is immobile, there is no displacement and therefore no work is being done by Elio. The same applies to Jordan as well. Therefore, no work is being done by either Elio or Jordan.

7. In which case is negative work done?

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

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.

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

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

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

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Explanation

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8. 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?

–14.7 J

+1.50 J

–1.50 J

+0.153 J

+14.7 J

When the person lifts the pail of water from the ground to the deck, they are doing work against the force of gravity. The work done by gravity is equal to the negative of the work done by the person. Since the work done by the person is positive (as they are lifting the pail), the work done by gravity is negative. Therefore, the correct answer is –14.7 J.

Explanation

When the person lifts the pail of water from the ground to the deck, they are doing work against the force of gravity. The work done by gravity is equal to the negative of the work done by the person. Since the work done by the person is positive (as they are lifting the pail), the work done by gravity is negative. Therefore, the correct answer is –14.7 J.

9. 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 ´ 10² N is

–4.00 x 102 J

+4.00 x 102 J

+1.00 x 102 J

–1.00 x 102 J

+1.00 x 104 J

The negative sign in the answer indicates that work is done against the force of the bullet. When work is done against a force, the work done is negative. Therefore, the correct answer is -1.00 x 102 J.

Explanation

The negative sign in the answer indicates that work is done against the force of the bullet. When work is done against a force, the work done is negative. Therefore, the correct answer is -1.00 x 102 J.

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?

As the basketball rises, its kinetic energy decreases

As the basketball rises, it is accelerated downward

As the basketball rises, its potential energy increases

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

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

As the basketball rises, its kinetic energy decreases. As the basketball moves upward, it loses speed and its kinetic energy decreases. However, its potential energy increases as it gains height. When the basketball reaches the top of its flight, its kinetic energy is not zero but rather at its minimum point. At the top, the basketball momentarily stops moving upward and starts moving downward, so its kinetic energy is not zero. The statement that when the basketball reaches the top of its flight, its kinetic energy is zero is false.

Explanation

As the basketball rises, its kinetic energy decreases. As the basketball moves upward, it loses speed and its kinetic energy decreases. However, its potential energy increases as it gains height. When the basketball reaches the top of its flight, its kinetic energy is not zero but rather at its minimum point. At the top, the basketball momentarily stops moving upward and starts moving downward, so its kinetic energy is not zero. The statement that when the basketball reaches the top of its flight, its kinetic energy is zero is false.

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

Twice as great

The same

Four times as great

Half as great

Cannot be calculated using the given information

If Nicholas exerts a certain force to lift the dumbbell 3.0 m above his head in 20 s, it means that he is using a certain amount of energy to do so. 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 remains the same, the energy required to lift the dumbbell would also be the same. Therefore, the correct answer is "the same".

Explanation

If Nicholas exerts a certain force to lift the dumbbell 3.0 m above his head in 20 s, it means that he is using a certain amount of energy to do so. 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 remains the same, the energy required to lift the dumbbell would also be the same. Therefore, the correct answer is "the same".

12. In the following figure, a 0.60-kg ball is about to fall to the step below.