Q: A construction worker lifts a 20 kg bag of cement to a height of 3 meters. What is the gravitational potential energy gained by the bag? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

$$PE = 20 \times 9.8 \times 3 = 588\ \mathrm{J}$$

Question 1

A person pushes against a stationary wall for several minutes, as shown in the image. According to the definition of work in physics, how much work is done on the wall?

Accepted Answer

No work is done because the wall does not move.

Question 2

A construction worker lifts a 20 kg bag of cement to a height of 3 meters. What is the gravitational potential energy gained by the bag? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$PE = 20 	imes 9.8 	imes 3 = 588\ \mathrm{J}$$

Question 3

A weightlifter raises a barbell from the floor to above their head, as shown in the image. Which of the following best describes the work done on the barbell?

Accepted Answer

Work is done because a force is applied over a vertical distance.

Question 4

A car is hoisted for repairs in a service station, as shown in the image. Compared to when it was on the ground, the car now has:

Accepted Answer

Increased potential energy relative to the floor.

Question 5

A 10-N ball is lifted to a height of 3 meters by three different paths: straight up, along a ramp, and up a set of stairs. Which statement is correct about the work done against gravity?

Accepted Answer

The work done is the same for all three paths.

Question 6

A rocket launches vertically, as shown in the image. Which form of energy increases most as the rocket gains altitude?

Accepted Answer

Gravitational potential energy

Question 7

A bow is drawn, storing 50 J of potential energy. When the arrow is released, it leaves the bow with 40 J of kinetic energy. What happened to the remaining energy?

Accepted Answer

It was converted to heat in the bow.

Question 8

A car with mass $$m is $$moving at velocity $$v. $$What is its kinetic energy?

Accepted Answer

$$KE = \frac{1}{2}mv^2$

Question 9

If the speed of a moving object is doubled, how does its kinetic energy change?

Accepted Answer

It quadruples.

Question 10

A car traveling at 20 m/s comes to a stop due to friction. If the initial speed of the car were doubled, how would the stopping distance change, assuming the same friction force?

Accepted Answer

It would be four times as long.

Question 11

Which equation best expresses the work-energy theorem?

Accepted Answer

$$W = \Delta KE$$

Question 12

A machine does 500 J of work in 10 seconds. What is its power output?

Accepted Answer

$$P = 500 / 10 = 50\ \mathrm{W}$$

Question 13

Which of the following statements about energy conservation is correct?

Accepted Answer

Energy can be transformed from one form to another, but the total amount remains constant.

Question 14

A person pushes a cart with a constant force over twice the distance. How does the work done compare to pushing it over the original distance?

Accepted Answer

It is twice as much.

Question 15

Which of the following is a correct unit for power?

Accepted Answer

Watt (W)

Question 16

A pile driver lifts a heavy weight and then drops it onto a post. Which energy transformation occurs during the drop?

Accepted Answer

Potential energy to kinetic energy

Question 17

Which of the following best distinguishes kinetic energy from momentum?

Accepted Answer

Momentum can be canceled; kinetic energy cannot.

Question 18

A 5 kg object is moving at 4 m/s. What is its kinetic energy?

Accepted Answer

$$KE = \frac{1}{2} 	imes 5 	imes 4^2$ = 40\ \mathrm{J}$$

Question 19

Which of the following scenarios best illustrates the transformation of potential energy into kinetic energy?

Accepted Answer

A ball dropped from a height.

Energy, Work, and Power: Foundations of Mechanical Energy

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