Question 1

Which of the following statements correctly distinguishes between conservative and nonconservative forces?

Accepted Answer

A conservative force does zero net work on an object moved around any closed path, while a nonconservative force does nonzero net work on a closed path.

Question 2

A 2.0 kg object is lifted vertically by 3.0 m. What is the change in its gravitational potential energy? (Assume $$g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$\Delta U = 58.8 \ \mathrm{J}$$

Question 3

Which equation correctly expresses the relationship between work done by a conservative force and the change in potential energy?

Accepted Answer

$$W = -\Delta U$$

Question 4

A spring with force constant $$k = 500 \ \mathrm{N/m} is $$compressed by $$0.10 \ \mathrm{m}. $$What is the elastic potential energy stored in the spring?

Accepted Answer

$$U = 2.5 \ \mathrm{J}$$

Question 5

A 0.15 kg baseball is hit and caught at a height 7.2 m above its starting point. Ignoring air resistance, what is the change in its gravitational potential energy?

Accepted Answer

$$\Delta U = 10.6 \ \mathrm{J}$$

Question 6

Which of the following is NOT a conservative force?

Accepted Answer

Friction

Question 7

A hiker climbs a mountain, gaining 1000 m in altitude. If the hiker's mass is 70 kg, what is the increase in gravitational potential energy? ($$g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$\Delta U = 686,000 \ \mathrm{J}$$

Question 8

Which formula represents the total mechanical energy of a system with only conservative forces?

Accepted Answer

$$E = U + K$$

Question 9

A 0.120 kg graduation cap is thrown upward with an initial speed of $$7.88 \ \mathrm{m/s}. $$What is its kinetic energy at the moment it leaves the hand?

Accepted Answer

$$K = 3.73 \ \mathrm{J}$$

Question 10

If a spring is stretched by $$x$$ from its equilibrium position, which equation gives its potential energy?

Accepted Answer

$$U = \frac{1}{2} k x^2$

Question 11

A cyclist and bicycle together have a mass of 70.3 kg. If the cyclist consumes a candy bar with $$8.16 	imes 10^5$ \ \mathrm{J} of $$energy and converts all of it to gravitational potential energy, what altitude could she reach?

Accepted Answer

$$h = 1,163 \ \mathrm{m}$$

Question 12

Which statement about the work done by friction is correct?

Accepted Answer

The work done by friction on a closed path is not zero and depends on the path taken.

Question 13

A block slides down a hill and comes to rest due to friction. Which statement best describes the energy transformation?

Accepted Answer

Mechanical energy is converted into thermal energy by the nonconservative force of friction.

Question 14

Which equation correctly describes the change in mechanical energy when nonconservative forces are present?

Accepted Answer

$$W_{nc} = \Delta E = \Delta U + \Delta K$$

Question 15

A spring with $$k = 740 \ \mathrm{N/m} is $$compressed by $$0.21 \ \mathrm{m}. $$What is the potential energy stored in the spring?

Accepted Answer

$$U = 16.3 \ \mathrm{J}$$

Question 16

Which of the following best describes a potential energy curve?

Accepted Answer

A graph of potential energy $$U$$ versus position, showing how energy changes as an object moves.

Question 17

A 1250 kg set of weights is lifted 2 m in a weightlifting contest. What potential energy do the weights possess at the new height?

Accepted Answer

$$U = 24,500 \ \mathrm{J}$$

Question 18

Which of the following is true about mechanical energy in a system with only conservative forces?

Accepted Answer

Mechanical energy is conserved and remains constant.

Question 19

A block of mass $$m is $$released from rest at height $$h$$ and slides down a frictionless incline. What is its speed at the bottom?

Accepted Answer

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

Potential Energy and Conservation of Energy (Physics Chapter 8 Study Notes)

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