Q: A 15 kg cannonball is launched straight up with a speed of 25 m/s. What is the maximum height it will reach? (Ignore air resistance)

$$h = \frac{v^2$}{2g} = \frac{(25)^2$}{2 \times 10} = 31.25\ \text{m}$$

Q: A 10 kg block is pushed across a friction-free floor by a horizontal force of 50 N for 7 meters in 4 seconds. What is the power used?

$$P = \frac{W}{t} = \frac{F \times d}{t} = \frac{50 \times 7}{4} = 87.5\ \text{W}$$

Q: A 5.0 kg rock is dropped from a cliff 90 meters high. After falling 20 meters, what is its kinetic energy?

$$KE = mgh = 5.0 \times 10 \times 20 = 1000\ \text{J}$$

Q: At an amusement park, a roller coaster train of mass 3500 kg ascends a 40 m hill. How much work is required to get the train from the ground to the top?

$$W = mgh = 3500 \times 10 \times 40 = 1,400,000\ \text{J}$$

Q: What is the potential energy stored in a bow when Diana pulls the arrow back 0.30 m with a force of 150 N?

$$PE = F \times d = 150 \times 0.30 = 45\ \text{J}$$

Q: A 18 kg object is lifted 4 meters off the ground in 5 seconds. What is the power required?

$$P = \frac{W}{t} = \frac{mgh}{t} = \frac{18 \times 10 \times 4}{5} = 144\ \text{W}$$

Q: Cinnamon, a cat of mass 5.45 kg, lands with a kinetic energy of 85.5 J after falling from a refrigerator. How tall is the refrigerator?

$$h = \frac{KE}{mg} = \frac{85.5}{5.45 \times 10} = 1.57\ \text{m}$$

Question 1

Which equation correctly defines 'work' in physics when a constant force is applied over a distance?

Accepted Answer

$$W = F 	imes d$$

Question 2

A 15 kg cannonball is launched straight up with a speed of 25 m/s. What is the maximum height it will reach? (Ignore air resistance)

Accepted Answer

$$h = \frac{v^2$}{2g} = \frac{(25)^2$}{2 	imes 10} = 31.25\ 	ext{m}$$

Question 3

What is the definition of 'power' in physics?

Accepted Answer

Power is the rate at which work is done.

Question 4

A 10 kg block is pushed across a friction-free floor by a horizontal force of 50 N for 7 meters in 4 seconds. What is the power used?

Accepted Answer

$$P = \frac{W}{t} = \frac{F 	imes d}{t} = \frac{50 	imes 7}{4} = 87.5\ 	ext{W}$$

Question 5

According to the Work-Energy Theorem, the work done on an object is equal to:

Accepted Answer

The change in kinetic energy of the object.

Question 6

A 5.0 kg rock is dropped from a cliff 90 meters high. After falling 20 meters, what is its kinetic energy?

Accepted Answer

$$KE = mgh = 5.0 	imes 10 	imes 20 = 1000\ 	ext{J}$$

Question 7

If a car traveling at 30 mph will skid 10 meters when its brakes lock, how far will it skid if it is traveling at 60 mph?

Accepted Answer

40 meters

Question 8

Two people, Bert and Ernie, who weigh the same, climb a flight of stairs. Bert climbs in 30 seconds, Ernie in 20 seconds. Who uses more power?

Accepted Answer

Ernie uses more power.

Question 9

A hammer falls off a rooftop and strikes the ground with a certain amount of kinetic energy. If it fell from a roof that was 4 times higher, how would its kinetic energy at impact compare?

Accepted Answer

It would be 4 times higher.

Question 10

Which graph best represents the relationship between kinetic energy and speed for a freely falling object?

Accepted Answer

A curve showing $$KE \propto v^2$

Question 11

At an amusement park, a roller coaster train of mass 3500 kg ascends a 40 m hill. How much work is required to get the train from the ground to the top?

Accepted Answer

$$W = mgh = 3500 	imes 10 	imes 40 = 1,400,000\ 	ext{J}$$

Question 12

What is the potential energy stored in a bow when Diana pulls the arrow back 0.30 m with a force of 150 N?

Accepted Answer

$$PE = F 	imes d = 150 	imes 0.30 = 45\ 	ext{J}$$

Question 13

A 18 kg object is lifted 4 meters off the ground in 5 seconds. What is the power required?

Accepted Answer

$$P = \frac{W}{t} = \frac{mgh}{t} = \frac{18 	imes 10 	imes 4}{5} = 144\ 	ext{W}$$

Question 14

Cinnamon, a cat of mass 5.45 kg, lands with a kinetic energy of 85.5 J after falling from a refrigerator. How tall is the refrigerator?

Accepted Answer

$$h = \frac{KE}{mg} = \frac{85.5}{5.45 	imes 10} = 1.57\ 	ext{m}$$

Question 15

For a pendulum, what is the only factor that determines how many complete swings it will make in one minute (ignoring friction)?

Accepted Answer

The length of the pendulum.

Question 16

A roller coaster car is at point A, 23 meters above the ground, moving at 17 m/s. At point B, it is moving at 21 m/s. How high above the ground is point B?

Accepted Answer

$$h_B = h_A + \frac{v_A^2$ - v_B^2$}{2g} = 23 + \frac{(17^2$ - 21^2$)}{2 	imes 10} = 20\ 	ext{m}$$

Question 17

What happens to the energy of a pendulum as it eventually slows down and stops?

Accepted Answer

Its mechanical energy is converted into thermal energy due to friction and air resistance.

Question 18

A 15 kg cannonball is launched straight up with a speed of 25 m/s. How much work was done on the cannonball to get it to its maximum height?

Accepted Answer

$$W = KE = \frac{1}{2}mv^2$ = \frac{1}{2} 	imes 15 	imes 25^2$ = 4687.5\ 	ext{J}$$

Physics Study Guide: Work, Energy, and Power

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