Question 1

A ball of mass $$m is $$dropped from a height $$h$$ above the ground. Neglecting air resistance, which of the following correctly describes the energy transformation as the ball falls?

Accepted Answer

Potential energy is converted into kinetic energy, and the total mechanical energy remains constant.

Question 2

Which of the following equations correctly gives the gravitational potential energy of an object of mass $$m at $$height $$y$$ above the ground?

Accepted Answer

$$U_g = mgy$$

Question 3

A mass oscillates on a horizontal spring. At which point in its motion is its kinetic energy the greatest?

Accepted Answer

At the equilibrium position, where the spring is neither stretched nor compressed.

Question 4

In an energy diagram, what does the vertical distance between the total energy line $$E$$ and the potential energy curve $$U at a $$given position represent?

Accepted Answer

The kinetic energy at that position.

Question 5

A collision in which two objects stick together and move with a common velocity after impact is called:

Accepted Answer

A perfectly inelastic collision.

Question 6

Which of the following is true for a perfectly elastic collision between two objects?

Accepted Answer

Both momentum and mechanical energy are conserved.

Question 7

Two railroad cars, one of mass $$2.0 	imes 10^4$ kg moving at 1.5$ m/s and another of mass 4.0$$ 	imes $$10^4 kg $$moving at $$-1.1 m/s$$, collide and couple together. What is the total kinetic energy lost (converted to thermal energy) during the collision?

Accepted Answer

$$4.5 	imes 10^3$ J

Question 8

A $$100 kg $$weightlifter raises a $$190 kg $$bar to a height of $$1.9 m in$$ $$1.8 s. $$What is the average power output during the lift? (Use $$g = 9.8 m/s$^2)$$

Accepted Answer

$$2000 W$$

Question 9

Which of the following best describes the equilibrium position in a potential energy diagram?

Accepted Answer

A position where the potential energy curve has a local minimum or maximum.

Question 10

A force $$F$$ acts on an object moving at velocity $$v. $$What is the output power delivered by the force?

Accepted Answer

$$P = Fv$$

Question 11

A $$0.2 kg $$toy car accelerates from rest to $$3 m/s in$$ $$2 s. $$What is the average power output during this acceleration?

Accepted Answer

$$0.6 W$$

Question 12

Which of the following statements about energy conservation in collisions is correct?

Accepted Answer

Momentum is always conserved, but mechanical energy is only conserved in perfectly elastic collisions.

Question 13

A mass $$m$$ attached to a spring with spring constant $$k$$ oscillates horizontally. What is the expression for the elastic potential energy stored in the spring when it is stretched by $$x$$?

Accepted Answer

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

Question 14

In a perfectly elastic head-on collision between two identical air hockey pucks, one moving at $$2.3 m/s $$and the other at rest, what are their velocities after the collision?

Accepted Answer

The moving puck stops, and the stationary puck moves at $$2.3 m/s.$$

Question 15

Which of the following is the correct definition of power in terms of energy?

Accepted Answer

$$P = \frac{\Delta E}{\Delta t}$$

Question 16

A particle moves in a potential energy well. At which point is its speed maximum?

Accepted Answer

Where the potential energy is at a minimum.

Question 17

Which of the following best describes thermal energy in the context of collisions?

Accepted Answer

Thermal energy is the sum of the microscopic kinetic and potential energies of all molecules in an object.

Question 18

A student runs up a flight of stairs of height $$h in $$time $$t. If $$the student’s mass is $$m$$, which expression gives the average power output?

Accepted Answer

$$P = \frac{mgh}{t}$$

Question 19

Which of the following is NOT a correct statement about energy diagrams?

Accepted Answer

The object can exist at a position where the potential energy curve is above the total energy line.

Energy Diagrams, Collisions, and Power: Study Notes for College Physics

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