Q: A 25 N box is carried up a staircase to a height of 2 meters in 5 seconds. What is the average power exerted during this process?

$$P = \frac{W}{t} = \frac{25 \times 2}{5} = 10\ \text{W}$$

Q: If the work required to lift a box to the second floor is equal to the potential energy it has at that height, what is the work required to lift a 50 N box up 3 meters?

$$W = 50 \times 3 = 150\ \text{J}$$

Question 1

When lifting a box of mass $$m up a $$flight of stairs to a height $$h$$, which of the following best describes the work done by you against gravity?

Accepted Answer

$$W = mgh$$

Question 2

A 25 N box is carried up a staircase to a height of 2 meters in 5 seconds. What is the average power exerted during this process?

Accepted Answer

$$P = \frac{W}{t} = \frac{25 	imes 2}{5} = 10\ 	ext{W}$$

Question 3

If you slide a box down the stairs, which force is responsible for doing work on the box?

Accepted Answer

Gravity

Question 4

You carry a box horizontally down a hallway at constant velocity for 3 meters. What is the work done by you on the box?

Accepted Answer

$$W = 0$$

Question 5

If you drop a 50 N box from a height of 3 meters, what is the velocity of the box just before it hits the ground? (Ignore air resistance)

Accepted Answer

$$v = \sqrt{2gh}$$

Question 6

Which of the following correctly expresses the relationship between potential energy (PE) and kinetic energy (KE) for a box dropped from height $$h$$?

Accepted Answer

$$PE = KE$$

Question 7

A box is lifted to a height $$h$$ and then dropped. Which equation gives the final velocity $$v in $$terms of $$g$$ and $$h$$?

Accepted Answer

$$v = \sqrt{2gh}$$

Question 8

If you run a 25 N box up the stairs in 3 seconds, what is the power exerted? If you take 10 seconds, what happens to the power?

Accepted Answer

Power decreases as time increases

Question 9

Which of the following best describes the energy transformation when a box is dropped from a height?

Accepted Answer

Potential energy is converted to kinetic energy

Question 10

If you carry a box up the stairs and then let it descend, how much work can the box do upon descending?

Accepted Answer

It can do an amount of work equal to the potential energy gained, $$W = mgh$$

Question 11

A box of weight $$W is $$lifted to a height $$h. $$What is the expression for its gravitational potential energy?

Accepted Answer

$$PE = W h$$

Question 12

If the work required to lift a box to the second floor is equal to the potential energy it has at that height, what is the work required to lift a 50 N box up 3 meters?

Accepted Answer

$$W = 50 	imes 3 = 150\ 	ext{J}$$

Question 13

Which of the following is true about the work done when carrying a box horizontally at constant velocity?

Accepted Answer

No work is done because the force is perpendicular to the displacement

Question 14

If you drop a box from the second floor, who does the work on the box?

Accepted Answer

Gravity

Question 15

A box of mass $$m is $$dropped from height $$h. $$Which kinematic equation can be used to find its final velocity?

Accepted Answer

$$v^2$$ = $$v_0^2 + 2gh$

Question 16

If the potential energy of a box is converted entirely into kinetic energy as it falls, which equation relates the two?

Accepted Answer

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

Question 17

If you slide a box down the stairs, how much work will have been done on the box by gravity?

Accepted Answer

$$W = mgh$$

Question 18

When carrying a box up the stairs, which force must you overcome to do work?

Accepted Answer

Gravity

Question 19

If you drop a box from a height, is the work done by gravity positive or negative?

Accepted Answer

Positive, because gravity does work in the direction of motion

Question 20

If you lift a box to a height $$h$$ and then drop it, what is the final velocity of the box upon reaching the ground using the potential energy approach?

Accepted Answer

$$v = \sqrt{2gh}$$

Work, Energy, and Forces: Study Notes for Physics

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