Pre AP Physics Chapter 5: Work and Energy

Multiple Choice (60)

Identify the letter of the choice that best completes the statement or answers the question. Carefully place your answer choice on your scantron answer document.

1. The equation for power can be written

a.	P = Ft	c.	P = Fv
b.	P = F/t	d.	P = F/v

2. The equation for work is W =

a.	Fv	c.	1/2 mv^2
b.	Fd	d.	mgh

3. What is the kinetic energy of a 65 kg student running at 3 m/s?

a.	97.5 J	c.	292.5 J
b.	195 J	d.	585 J

4. For kinetic energy mass and kinetic energy are related

a.	inversely.	c.	directly.
b.	quadradically.	d.	indirectly.

5. A ball is thrown up into the air. Negating air resistance which statement correctly describes the gravitational potential energy and the kinetic energy of the object?

a.	At all times the sum of these two energies is equal.	c.	For half the time both of these energies increase together.
b.	At all times the quantity of these two energies is the same.	d.	For half the time there is no kinetic energy and for the other half there is no gravitational potential energy.

6. Consider the equation for gravitational potential energy. If the GPE remains constant and one of the terms in the equation triples

a.	at least one other term must also triple.	c.	both other terms must be reduced by one third each of their original value.
b.	at least one other term must be reduced to one third it original value.	d.	one other term must increase by one third and the other term must be reduced by one third.

7. For kinetic energy mass and kinetic energy are related

a.	inversely.	c.	directly.
b.	quadradically.	d.	indirectly.

8. Under what condition is mechanical energy not conserved?

a.	for objects in free fall	c.	for situations involving the normal force.
b.	for objects in circular orbit	d.	for situations involving the force of friction.

9. According to the equation for elastic potential energy the energy potential of a spring is a function of

a.	the mass on the spring.	c.	the distance the spring is stretched.
b.	the mass and the distance the spring is stretched.	d.	the square of the magnitude to which the spring is stretched.

10. In order for work to be done it is only necessary that

a.	motion occur.
b.	a force be applied.
c.	a force moves through a distance
d.	energy be moving through a distance

11. For a projectile work is done

a.	only in the horizontal direction.	c.	both in the horizontal and vertical direction.
b.	only in the vertical direction.	d.	neither in the horizontal nor vertical direction.

12. Kinetic energy cannot be negative because

a.	energy is a vector.	c.	mass is squared.
b.	energy is a scalar.	d.	velocity is squared.

13. A kilowatt-hour is actually

a.	3.6 x 10^6 J	c.	3.6 x 10^6 J/s
b.	3.6 x 10^6 Js	d.	3.6 x 10^6 J s

14. A dropped ball never bounces back to the height from which it was dropped. This is because

a.	balls are not perfectly round.	c.	there is air resistance.
b.	floors are not perfectly flat.	d.	energy is conserved.

15. According to the Work-Kinetic Energy Theorem Work is equal to

a.	kinetic energy.	c.	one over kinetic energy.
b.	kinetic energy squared	d.	change in kinetic energy.

16. Consider the equation for elastic potential energy. The SI units for the ‘k’ are

a.	m/N	c.	Nm
b.	N/m	d.	Nm^2

17. The kinetic energy of a falling object

a.	always increases.	c.	comes from the mass of the object.
b.	always decreases.	d.	comes from the inertia of the object.

18. Consider a situation wherein an object moving at 20 m/s comes to a stop. The change in velocity of this object is equal to

a.	1/2 20 m/s	c.	20 m/s
b.	1/2 20 m/s^2	d.	20 m/s^2

19. Which of these cannot do work on an object?

a.	a perpendicular force	c.	a balanced force
b.	the force of friction	d.	the force of gravity

20. No work is done on a satellite in circular orbit because

a.	satellites are weightless in space.	c.	there is no gravity in space.
b.	the force of gravity is parallel to the satellite’s orbit.	d.	the force of gravity is perpendicular to the satellite’s orbit.

Short Answer (100)

Answer the questions below on your own paper. Questions in 'a', 'b', 'c' format must be answered in 'a', 'b', 'c' format. Each question must be answered on its own page. Do not answer more than one question on a page. Since this section has five questions you should have five pages for you answers.

21. Consider the conservation of energy of a falling object.

a) Write the general equation that shows energy is conserved in this situation.

b) Write the equations from part ‘a’ again so that one can clearly see that one of the quantities can be removed form the equation. Write out which quantity this is.

c) Write the equation from part ‘b’ for velocity and use this equation to prove that regardless of mass all objects dropped from the same height must have the same final velocity.

d) Consider two objects ‘x’ and ‘y’. The final velocity of ‘y’ is twice the final velocity of ‘x’. How much higher than ‘x’ was ‘y’ dropped?

e) Consider two objects ‘p’ and ‘q’. Object ‘q’ is dropped from a height that is twice that of ‘p’. By what factor is the final velocity of ‘q’ greater than the final velocity of ‘p’?

22. Consider a person walking along a horizontal floor and then descending a flight of stairs.

a) In what direction is gravity acting as the person walks along the horizontal floor?

b) How much work, if any, is gravity doing on the person walking along the horizontal floor?

c) In what direction is gravity acting as the person descends the stairs?

d) How much work, if any, is gravity doing on the person as they walk down the stairs?

e) Explain why more energy is needed to walk down a flight of stairs than is needed to walk across a horizontal floor.

Pre AP Physics Chapter 5: Work and Energy

Answer Section

MULTIPLE CHOICE

1. C

2. B

3. C

4. C

5. A

6. B

7. B

8. D

9. D

10. C

11. B

12. D

13. A

14. D

15. D

16. B

17. A

18. C

19. A

20. D

SHORT ANSWER

21. Considering the conservation of energy of a falling object.

a) The general equation showing that energy is conserved in this situation is GPE = KE.

b) The equation in ‘a’ written out so that one can clearly see that one of the quantities can be removed is mgh = 1/2mv². The quantity that can be removed is mass.

c) The equation from part ‘b’ solved for velocity is . Since there is no term for mass in this equation it must be concluded that all objects will have the same final velocity when dropped from the same height.

d) If object ‘y’ has twice the final velocity of ‘x’ it must have been dropped from a height four times that of ‘x’.

e) If the height of ‘q’ = 2h’p’ than the final velocity of ‘q’ will be greater than the final velocity of ‘p’.

22. Considering a person walking along a horizontal floor and then descending a flight of stairs.

a) As a person walks along a horizontal floor gravity is acting straight down or perpendicular to the direction of the person’s motion.

b) As a person walks along a horizontal floor gravity can not do any work on the person since gravity acts perpendicular to the direction of the person’s motion.

c) As the person walks down the stairs gravity acts straight down, in a direction to the direction of motion.

d) Gravity is doing work on the person as they walk down the stairs. The magnitude of the force of gravity is . Or, the product of the weight of the person and of the stairs.

e) More energy is needed to walk down a stair case than to walk across a horizontal floor because gravity does no work on you if you walk across a horizontal floor. But, as you descend a staircase you must do work against gravity. This work done against gravity for the height of the staircase is the energy you must expend walking down the stairs.