Q: A roller coaster car starts from rest at the top of a 60 m high hill (see $$image_1). $$Ignoring friction and air resistance, what is the speed of the car at the bottom of the hill? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

$$v = \sqrt{2gh} = \sqrt{2 \times 9.8 \times 60} = 34.3\ \mathrm{m/s}$$

Q: A dog pulls a sled with a force of 350 N over a distance of 4.9 m at constant speed (see $$image_15). $$How much work does the dog do?

$$W = Fd = 350 \times 4.9 = 1715\ \mathrm{J}$$

Q: A 30.0-kg package moves at $$0.500\ \mathrm{m/s} on a $$conveyor belt. What is its kinetic energy?

$$K = \frac{1}{2}mv^2$ = \frac{1}{2} \times 30.0 \times (0.500)^2$ = 3.75\ \mathrm{J}$$

Q: A force of 120 N pushes a 30.0-kg package 0.800 m against a friction force of 5.00 N. What is the net work done on the package?

$$W = (F_{\text{push}} - F_{\text{friction}})d = (120 - 5) \times 0.800 = 92\ \mathrm{J}$$

Q: A 2.0 kg object is lifted vertically by 5.0 m. What is the change in its gravitational potential energy? ($$g = 9.8\ \mathrm{m/s^2$})$$

$$\Delta U_g = mgh = 2.0 \times 9.8 \times 5.0 = 98\ \mathrm{J}$$

Q: A spring with a spring constant $$k = 200\ \mathrm{N/m} is $$compressed by $$0.10\ \mathrm{m}. $$What is the elastic potential energy stored in the spring?

$$U_s = \frac{1}{2}kx^2$ = \frac{1}{2} \times 200 \times (0.10)^2$ = 1.0\ \mathrm{J}$$

Q: A 10 kg box is pulled 5 m across a frictionless floor by a 20 N force at an angle of $$60^\circ$$ above the horizontal. How much work is done by the force?

$$W = Fd\cos\theta = 20 \times 5 \times \cos 60^\circ = 50\ \mathrm{J}$$

Q: A 0.010 kg ball is launched horizontally by a spring with $$k = 10\ \mathrm{N/m}$$ compressed by $$0.10\ \mathrm{m}. $$What is the speed of the ball as it leaves the spring?

$$v = \sqrt{\frac{kx^2$}{m}} = \sqrt{\frac{10 \times (0.10)^2$}{0.010}} = 3.2\ \mathrm{m/s}$$

Question 1

A roller coaster car starts from rest at the top of a 60 m high hill (see $$image_1). $$Ignoring friction and air resistance, what is the speed of the car at the bottom of the hill? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$v = \sqrt{2gh} = \sqrt{2 	imes 9.8 	imes 60} = 34.3\ \mathrm{m/s}$$

Question 2

A dog pulls a sled with a force of 350 N over a distance of 4.9 m at constant speed (see $$image_15). $$How much work does the dog do?

Accepted Answer

$$W = Fd = 350 	imes 4.9 = 1715\ \mathrm{J}$$

Question 3

Which of the following best describes the energy transformation when a diver jumps off a springboard (see $$image_6$$)?

Accepted Answer

Elastic potential energy is converted to kinetic energy, then to gravitational potential energy.

Question 4

A 30.0-kg package moves at $$0.500\ \mathrm{m/s} on a $$conveyor belt. What is its kinetic energy?

Accepted Answer

$$K = \frac{1}{2}mv^2$ = \frac{1}{2} 	imes 30.0 	imes (0.500)^2$ = 3.75\ \mathrm{J}$$

Question 5

A force of 120 N pushes a 30.0-kg package 0.800 m against a friction force of 5.00 N. What is the net work done on the package?

Accepted Answer

$$W = (F_{	ext{push}} - F_{	ext{friction}})d = (120 - 5) 	imes 0.800 = 92\ \mathrm{J}$$

Question 6

A 2.0 kg object is lifted vertically by 5.0 m. What is the change in its gravitational potential energy? ($$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$\Delta U_g = mgh = 2.0 	imes 9.8 	imes 5.0 = 98\ \mathrm{J}$$

Question 7

A spring with a spring constant $$k = 200\ \mathrm{N/m} is $$compressed by $$0.10\ \mathrm{m}. $$What is the elastic potential energy stored in the spring?

Accepted Answer

$$U_s = \frac{1}{2}kx^2$ = \frac{1}{2} 	imes 200 	imes (0.10)^2$ = 1.0\ \mathrm{J}$$

Question 8

A 10 kg box is pulled 5 m across a frictionless floor by a 20 N force at an angle of $$60^\circ$$ above the horizontal. How much work is done by the force?

Accepted Answer

$$W = Fd\cos	heta = 20 	imes 5 	imes \cos 60^\circ = 50\ \mathrm{J}$$

Question 9

Which of the following forces does NO work on an object?

Accepted Answer

A force perpendicular to the displacement.

Question 10

A 0.010 kg ball is launched horizontally by a spring with $$k = 10\ \mathrm{N/m}$$ compressed by $$0.10\ \mathrm{m}. $$What is the speed of the ball as it leaves the spring?

Accepted Answer

$$v = \sqrt{\frac{kx^2$}{m}} = \sqrt{\frac{10 	imes (0.10)^2$}{0.010}} = 3.2\ \mathrm{m/s}$$

Question 11

A 190 kg barbell is lifted 1.9 m in 1.8 s. What is the average power output of the lifter? ($$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$P = \frac{mgh}{t} = \frac{190 	imes 9.8 	imes 1.9}{1.8} = 1962\ \mathrm{W}$$

Question 12

Two railroad cars, each of mass $$2.0 	imes 10^4$\ \mathrm{kg}$$, collide and couple together. One moves at $$1.5\ \mathrm{m/s}$$, the other at $$-1.1\ \mathrm{m/s}. $$What is the increase in thermal energy during the collision?

Accepted Answer

$$\Delta E_{th} = K_i - K_f = 4.7 	imes 10^4$\ \mathrm{J} - 1900\ \mathrm{J} = 4.5 	imes 10^4$\ \mathrm{J}$$

Question 13

A 1.0 kg box is pulled 10 m by a 10 N force, a 2.0 kg box by a 15 N force, a 0.5 kg box by a 50 N force, a 3.0 kg box by a 20 N force, and a 0.3 kg box by a 12 N force. Which box experiences the greatest change in kinetic energy?

Accepted Answer

The 0.5 kg box pulled by a 50 N force.

Question 14

A child on a swing is motionless at the highest point. As the swing moves down, what energy transformation occurs?

Accepted Answer

Gravitational potential energy is converted to kinetic energy.

Question 15

Which of the following statements about energy in an isolated system is correct?

Accepted Answer

The total energy remains constant, but energy can be transformed between different forms.

Question 16

A force acts at an angle $$	heta to $$the direction of displacement $$d. $$Which formula gives the work done by the force?

Accepted Answer

$$W = Fd\cos	heta$$

Chapter 10: Energy and Work – Physics with Algebra Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards