Q: A person pulls a sled with a force of 94.0 N at an angle of 25.0° above the horizontal for a distance of 35.0 m. What is the work done by the tension force?

$$W = 94.0 \times 35.0 \times \cos(25.0^\circ) = 2982 J$$

Q: A 55 kg block is pushed 70.0 m across a rough floor by a 160 N force parallel to the displacement. The coefficient of kinetic friction is 0.25. What is the net work done on the block?

$$W_{net} = 160 \times 70.0 - (0.25 \times 55 \times 9.8 \times 70.0) = 11200 - 9432.5 = 1767.5 J$$

Q: A toy snake has a spring with a force constant of 230 N/m. How much work is required to stretch the spring 2.5 cm?

$$W = \frac{1}{2} \times 230 \times (0.025)^2$ = 0.072 J$$

Question 1

A person pulls a sled with a force of 94.0 N at an angle of 25.0° above the horizontal for a distance of 35.0 m. What is the work done by the tension force?

Accepted Answer

$$W = 94.0 	imes 35.0 	imes \cos(25.0^\circ) = 2982 J$$

Question 2

Which of the following best describes the work done by friction when a box is pulled across a rough floor at constant speed?

Accepted Answer

Friction does negative work

Question 3

A 55 kg block is pushed 70.0 m across a rough floor by a 160 N force parallel to the displacement. The coefficient of kinetic friction is 0.25. What is the net work done on the block?

Accepted Answer

$$W_{net} = 160 	imes 70.0 - (0.25 	imes 55 	imes 9.8 	imes 70.0) = 11200 - 9432.5 = 1767.5 J$$

Question 4

Which of the following is the correct expression for the work done by a constant force at an angle $$	heta to $$the displacement?

Accepted Answer

$$W = Fd \cos 	heta$$

Question 5

A ball tied to a string is being whirled around in a circle. What is the work done by the tension force?

Accepted Answer

Tension does no work at all

Question 6

You lift a book with your hand so that it moves up at constant speed. What is the total work done on the book while it is moving?

Accepted Answer

$$W_{total} = 0$$

Question 7

According to the work-energy theorem, the total work done on an object is equal to:

Accepted Answer

Its change in kinetic energy

Question 8

A skier slides horizontally along the snow for 21 m before coming to rest. The coefficient of kinetic friction is $$\mu_k = 0.05. $$What was the skier's initial speed?

Accepted Answer

$$v_i = \sqrt{2 \mu_k g d}$$

Question 9

Is it possible for the kinetic energy of an object to be negative?

Accepted Answer

No, kinetic energy is always zero or positive

Question 10

The work done in stretching a spring by an amount $$x is $$given by:

Accepted Answer

$$W = \frac{1}{2}kx^2$

Question 11

A toy snake has a spring with a force constant of 230 N/m. How much work is required to stretch the spring 2.5 cm?

Accepted Answer

$$W = \frac{1}{2} 	imes 230 	imes (0.025)^2$ = 0.072 J$$

Question 12

Which of the following is the correct SI unit for power?

Accepted Answer

Watt (W)

Question 13

If an object is moving at a constant speed $$v$$ under a constant force $$F$$, what is the power exerted by the force?

Accepted Answer

$$P = Fv$$

Question 14

Mike applied 10 N of force over 3 m in 10 seconds. Joe applied the same force over the same distance in 1 minute. Who did more work?

Accepted Answer

Both did the same work

Question 15

Mike performed 5 J of work in 10 seconds. Joe did 3 J of work in 5 seconds. Who produced the greater power?

Accepted Answer

Joe produced more power

Question 16

A box is being pulled up a rough incline by a rope connected to a pulley. How many forces are doing work on the box?

Accepted Answer

Three forces

Question 17

Which of the following is the correct formula for kinetic energy?

Accepted Answer

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

Question 18

If the angle between the force and displacement is 90°, what is the work done?

Accepted Answer

Work is zero

Question 19

Which of the following activities requires the least amount of work according to Table 7-1?

Accepted Answer

Breaking a bond in DNA

Work, Kinetic Energy, and Power: Chapter 7 Study Notes

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드