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

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

Q: A tractor pulls a sled with a force of $$5000\ \mathrm{N} at an $$angle of $$36.9^\circ$$ over a distance of $$20\ \mathrm{m}. $$What is the work done by the tractor?

$$W = 5000 \times 20 \times \cos(36.9^\circ) = 80,000\ \mathrm{J}$$

Q: A 5 kg object is lifted vertically upward by 2 m. What is the change in its gravitational potential energy? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

$$\Delta U = mgh = 5 \times 9.8 \times 2 = 98\ \mathrm{J}$$

Question 1

Which of the following best describes the difference between conservative and non-conservative forces?

Accepted Answer

Conservative forces do not dissipate mechanical energy, while non-conservative forces convert mechanical energy into other forms such as heat.

Question 2

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

Accepted Answer

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

Question 3

A block is pushed across a rough surface and comes to rest. What happens to its initial kinetic energy?

Accepted Answer

It is converted into internal energy (heat) due to friction.

Question 4

A force $$\vec{F} is $$applied at an angle $$\phi to $$the direction of displacement $$\vec{s}. $$What is the formula for the work done by this force?

Accepted Answer

$$W = F s \cos \phi$$

Question 5

A tractor pulls a sled with a force of $$5000\ \mathrm{N} at an $$angle of $$36.9^\circ$$ over a distance of $$20\ \mathrm{m}. $$What is the work done by the tractor?

Accepted Answer

$$W = 5000 	imes 20 	imes \cos(36.9^\circ) = 80,000\ \mathrm{J}$$

Question 6

Which of the following is NOT a conservative force?

Accepted Answer

Frictional force

Question 7

A 5 kg object is lifted vertically upward by 2 m. What is the change in its gravitational potential energy? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$\Delta U = mgh = 5 	imes 9.8 	imes 2 = 98\ \mathrm{J}$$

Question 8

If the net work done on a particle is zero, what can be said about its kinetic energy?

Accepted Answer

Its kinetic energy remains constant.

Question 9

A runner climbs a staircase of height $$h in $$time $$\Delta t. $$What is the average power output if the runner's mass is $$m$$?

Accepted Answer

$$P_{av} = \frac{mgh}{\Delta t}$$

Question 10

Which equation correctly expresses the work-energy theorem?

Accepted Answer

$$W_{total} = \Delta K = K_f - K_i$$

Question 11

A block slides down a frictionless incline. Which of the following statements is true about its mechanical energy?

Accepted Answer

Its mechanical energy remains constant.

Question 12

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

Accepted Answer

The work is zero.

Question 13

Which of the following best describes the energy transformation when a car brakes to a stop?

Accepted Answer

Kinetic energy is converted into internal energy (heat) due to friction.

Question 14

A 10 kg box is pushed with a force of 50 N over a distance of 5 m. The force is applied parallel to the displacement. What is the work done?

Accepted Answer

$$W = 50 	imes 5 = 250\ \mathrm{J}$$

Question 15

Which of the following is the correct unit for power?

Accepted Answer

Watt (W)

Question 16

A sled of mass $$m is $$pulled by a force $$F_T at an $$angle $$\phi$$ above the horizontal. The friction force is $$f. $$What is the total work done on the sled over a displacement $$s$$?

Accepted Answer

$$W_{total} = (F_T \cos \phi - f) s$$

Question 17

Which of the following equations represents the conservation of mechanical energy for a system with only conservative forces?

Accepted Answer

$$K_i + U_i = K_f + U_f$$

Question 18

A 3 kg object starts from rest and a net work of 18 J is done on it. What is its final speed?

Accepted Answer

$$v_f = \sqrt{\frac{2 W_{total}}{m}} = \sqrt{\frac{2 	imes 18}{3}} = \sqrt{12} \approx 3.46\ \mathrm{m/s}$$

Work, Energy, and Power: Physics Study Guide

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