Q: A person pushes a stalled car with a constant force of 400 N for a distance of 15 m along a straight road. What is the total work done by the person on the car?

$$W = 400 \times 15 = 6000\ \mathrm{J}$$

Q: A force of 50 N acts at an angle of $$60^\circ to $$the direction of displacement of 10 m. What is the work done by the force?

$$W = 50 \times 10 \times \cos 60^\circ = 250\ \mathrm{J}$$

Q: A 2 kg object moves at 3 m/s. What is its kinetic energy?

$$K = \frac{1}{2} \times 2 \times 3^2$ = 9\ \mathrm{J}$$

Q: A spring with spring constant $$k = 200\ \mathrm{N/m} is $$stretched by $$0.5\ \mathrm{m}. $$What is the work done to stretch the spring?

$$W = \frac{1}{2} \times 200 \times (0.5)^2$ = 25\ \mathrm{J}$$

Q: A 100 kg elevator is lifted upward at constant speed through a height of 10 m in 5 seconds. What is the average power output required?

$$P_{av} = \frac{W}{\Delta t} = \frac{100 \times 9.8 \times 10}{5} = 1960\ \mathrm{W}$$

Q: A cyclist exerts a constant force of 200 N at an angle of $$30^\circ to $$the direction of motion over a distance of 50 m. What is the work done by the cyclist?

$$W = 200 \times 50 \times \cos 30^\circ = 8660\ \mathrm{J}$$

Question 1

A person pushes a stalled car with a constant force of 400 N for a distance of 15 m along a straight road. What is the total work done by the person on the car?

Accepted Answer

$$W = 400 	imes 15 = 6000\ \mathrm{J}$$

Question 2

A force of 50 N acts at an angle of $$60^\circ to $$the direction of displacement of 10 m. What is the work done by the force?

Accepted Answer

$$W = 50 	imes 10 	imes \cos 60^\circ = 250\ \mathrm{J}$$

Question 3

Which of the following scenarios results in zero work being done by a force?

Accepted Answer

A person holds a heavy box stationary above their head.

Question 4

A 2 kg object moves at 3 m/s. What is its kinetic energy?

Accepted Answer

$$K = \frac{1}{2} 	imes 2 	imes 3^2$ = 9\ \mathrm{J}$$

Question 5

If the speed of a car doubles, by what factor does its kinetic energy change?

Accepted Answer

It increases by a factor of 4.

Question 6

A weightlifter lowers a barbell to the floor. Which statement is true about the work done by the weightlifter's hands on the barbell?

Accepted Answer

The weightlifter's hands do negative work on the barbell.

Question 7

A spring with spring constant $$k = 200\ \mathrm{N/m} is $$stretched by $$0.5\ \mathrm{m}. $$What is the work done to stretch the spring?

Accepted Answer

$$W = \frac{1}{2} 	imes 200 	imes (0.5)^2$ = 25\ \mathrm{J}$$

Question 8

Which of the following best describes the work-energy theorem?

Accepted Answer

The net work done on a particle equals the change in its kinetic energy.

Question 9

A force $$F_x$$ varies with position $$x as $$shown on a graph. How is the total work done by the force from $$x_1 to$$ $$x_2$$ calculated?

Accepted Answer

$$W = \int_{x_1$}^{x_2$} F_x\ dx$$

Question 10

A 100 kg elevator is lifted upward at constant speed through a height of 10 m in 5 seconds. What is the average power output required?

Accepted Answer

$$P_{av} = \frac{W}{\Delta t} = \frac{100 	imes 9.8 	imes 10}{5} = 1960\ \mathrm{W}$$

Question 11

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

Accepted Answer

Watt ($$\mathrm{W})$$

Question 12

A cyclist exerts a constant force of 200 N at an angle of $$30^\circ to $$the direction of motion over a distance of 50 m. What is the work done by the cyclist?

Accepted Answer

$$W = 200 	imes 50 	imes \cos 30^\circ = 8660\ \mathrm{J}$$

Question 13

A 0.5 kg ball is thrown horizontally at 8 m/s. What is its kinetic energy?

Accepted Answer

$$K = \frac{1}{2} 	imes 0.5 	imes 8^2$ = 16\ \mathrm{J}$$

Question 14

Which statement about kinetic energy is correct?

Accepted Answer

Kinetic energy depends only on mass and speed, not on direction of motion.

Question 15

A car of mass $$m$$ increases its speed from $$v_1 to$$ $$v_2. $$What is the net work done on the car?

Accepted Answer

$$W_{tot} = \frac{1}{2} m v_2$^2 - \frac{1}{2} m v_1$^2$$

Question 16

A force acts perpendicular to the displacement of an object. What is the work done by this force?

Accepted Answer

Zero

Question 17

A machine does 500 J of work in 2 seconds. What is its average power output?

Accepted Answer

$$P_{av} = \frac{500}{2} = 250\ \mathrm{W}$$

Question 18

Which formula correctly expresses instantaneous power in terms of force and velocity?

Accepted Answer

$$P = \vec{F} \cdot \vec{v}$$

Question 19

A spring is stretched from $$x = 0 to$$ $$x = 0.2\ \mathrm{m}$$ with a spring constant $$k = 100\ \mathrm{N/m}. $$What is the work done on the spring?

Accepted Answer

$$W = \frac{1}{2} 	imes 100 	imes (0.2)^2$ = 2\ \mathrm{J}$$

Work and Kinetic Energy (Chapter 6): Study Notes

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드