Question 1

A hydroelectric dam stores water at a high elevation. Which form of energy is primarily responsible for the ability of the dam to generate electricity when water is released?

Accepted Answer

Gravitational potential energy of the water

Question 2

Two boxes connected by a spring are compressed and then released. If the spring is included as part of the system, which equation best describes the energy transformation?

Accepted Answer

$$\Delta E_{sys} = \Delta K + \Delta U = 0$$

Question 3

Which statement about potential energy is correct?

Accepted Answer

Potential energy is associated with interactions between objects.

Question 4

A ball of mass $$m is $$thrown upward. What is the expression for its gravitational potential energy at height $$y$$?

Accepted Answer

$$U_G = mgy$$

Question 5

Amber and Carlos measure the gravitational potential energy of a rock using different coordinate systems. Why do they report different values for $$U_G$$?

Accepted Answer

They set the zero of potential energy at different positions.

Question 6

A sled slides down a frictionless slope. Which force does no work on the sled?

Accepted Answer

Normal force

Question 7

When friction is present in a system, which statement is true about mechanical energy?

Accepted Answer

Mechanical energy decreases as some is transformed into thermal energy.

Question 8

A block attached to a spring slides on a frictionless surface. What is the expression for the elastic potential energy stored in the spring?

Accepted Answer

$$U_{Sp} = \frac{1}{2} k \Delta s^2$

Question 9

A system contains gravitational, elastic, and frictional interactions. Which equation correctly represents the energy principle for this system?

Accepted Answer

$$K_i + U_{G,i} + U_{Sp,i} = K_f + U_{G,f} + U_{Sp,f} + \Delta E_{th}$$

Question 10

Which statement best describes the Law of Conservation of Energy?

Accepted Answer

The total energy of an isolated system remains constant, though it can be transformed between kinetic, potential, and thermal forms.

Question 11

A 500 g glider compresses a spring by 2.7 cm before rebounding. If the spring constant is $$k$$, what is the initial speed of the glider?

Accepted Answer

$$v_i = \sqrt{\frac{k \Delta s^2$}{2m}}$$

Question 12

In an energy diagram, what does the point where the total energy line crosses the potential energy curve represent?

Accepted Answer

A turning point where the particle reverses direction

Question 13

For a mass oscillating on a spring, the potential energy graph is a parabola. What determines the width of the parabola?

Accepted Answer

The spring constant $$k$$

Question 14

If the potential energy $$U(x) is $$known as a function of position, how can the force in the $$x$$ direction be found?

Accepted Answer

$$F_x = -\frac{dU}{dx}$$

Question 15

Which of the following is a conservative force?

Accepted Answer

Gravitational force

Question 16

A pendulum is released from a height. At its lowest point, what is true about its speed compared to its initial speed?

Accepted Answer

It is maximum because all energy is kinetic.

Question 17

Which statement about equilibrium positions in an energy diagram is correct?

Accepted Answer

A maximum in the potential energy curve is a point of unstable equilibrium.

Question 18

A particle is placed at a point where the potential energy curve is above the total energy line. What happens?

Accepted Answer

The particle cannot be at that point.

Question 19

Which of the following best describes the work done by the normal force on an object sliding down a frictionless surface?

Accepted Answer

It is zero because the normal force is always perpendicular to the motion.

Question 20

Which equation represents the change in gravitational potential energy for a ball moving from $$y_i to$$ $$y_f$$?

Accepted Answer

$$\Delta U_G = mgy_f - mgy_i$$

Potential Energy and Energy Conservation in Physics

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