Q: A person lifts a 10 kg box vertically upward by 1.0 m in 5 seconds. What is the average power output?

$$P = \frac{mgd}{t} = \frac{10 \times 9.8 \times 1.0}{5} = 19.6\ \text{W}$$

Question 1

A ball of mass $$m is $$swung in a vertical circle at the end of a string of length $$R. At $$the top of the circle, what is the correct expression for the net centripetal force $$F_c$$ acting on the ball?

Accepted Answer

$$F_c = T + mg$$

Question 2

A skier of mass $$m$$ goes over a small round hill of radius $$R. At $$the very top of the hill, what is the correct expression for the net centripetal force $$F_c$$ acting on the skier?

Accepted Answer

$$F_c = mg - N$$

Question 3

A car travels up a hill of angle $$	heta$$ with respect to the horizontal at constant velocity $$v$$ for a distance $$d. $$What is the work done by the sum of the gravitational force and the constant upward frictional force exerted by the hill on the tires?

Accepted Answer

$$W = -(mg \sin 	heta) d$$

Question 4

Which of the following best describes the difference between walking and running up a flight of stairs, assuming you reach the same height in both cases?

Accepted Answer

The work done is the same, but the power output is greater when running.

Question 5

A sports car engine delivers constant power as it accelerates from rest. Neglecting air resistance, which graph best represents the speed $$v of $$the car as a function of time $$t$$?

Accepted Answer

A curve that increases with decreasing slope (square root function)

Question 6

A 1000 kg car starts from rest and is pushed by a force $$F$$ that varies with distance as shown in a graph. After traveling 500 m, the car's speed is found using the work-energy theorem. Which equation gives the final speed $$v$$?

Accepted Answer

$$v = \sqrt{\frac{2W}{m}}$$

Question 7

A lighter car and a heavier truck, both initially at rest, are pushed with the same constant force $$F$$ over the same distance $$d. $$Which statement is true?

Accepted Answer

They will have the same velocity.

Question 8

A lighter car and a heavier truck, both moving at the same speed $$v$$, apply the same constant braking force $$F$$ and travel the same distance $$d$$ before stopping. Which statement is true?

Accepted Answer

The work done on both vehicles is the same.

Question 9

You push a heavy crate down a ramp at constant velocity. Four forces act: gravity, normal force, friction, and your push. Which force does the greatest magnitude of work on the crate?

Accepted Answer

The force of friction

Question 10

Which equation correctly expresses the average power $$\overline{P}$$ delivered over a time interval $$\Delta t$$?

Accepted Answer

$$\overline{P} = \frac{\Delta W}{\Delta t}$$

Question 11

A spring with force constant $$k is $$stretched a distance $$X$$ from equilibrium. What is the work done by the spring as it is stretched from $$x=0 to$$ $$x=X$$?

Accepted Answer

$$W = \frac{1}{2}kX^2$

Question 12

A spring scale is calibrated so that a 1.50 kg mass stretches it by 1.00 cm. What is the spring constant $$k$$?

Accepted Answer

$$k = \frac{mg}{\Delta L}$$

Question 13

Which of the following is the correct expression for instantaneous power $$p$$?

Accepted Answer

$$p = \frac{dW}{dt}$$

Question 14

A child pulls a sled with constant speed, exerting a force $$F at an $$angle $$	heta$$ above the horizontal for a distance $$d. $$What is the work done by the friction force if the coefficient of friction is $$\mu$$ and the sled mass is $$m$$?

Accepted Answer

$$W = -\mu mg d$$

Question 15

A block is attached to a spring and pulled so that the spring is stretched by $$x. $$According to Hooke's Law, what is the force exerted by the spring?

Accepted Answer

$$F = -kx$$

Question 16

Which of the following statements about the work done by a spring is correct?

Accepted Answer

The work done by a spring is equal to the area under the force vs. displacement graph.

Question 17

A person lifts a 10 kg box vertically upward by 1.0 m in 5 seconds. What is the average power output?

Accepted Answer

$$P = \frac{mgd}{t} = \frac{10 	imes 9.8 	imes 1.0}{5} = 19.6\ 	ext{W}$$

Work, Kinetic Energy, Power, and Elastic Forces: Study Notes for Physics with Calculus

Study Guide - Practice Questions

Study Guide - Flashcards