Name: 
 

Momentum & Energy Review


Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
 

1. 
A child pulls a 7.4-kg toboggan 4.2 m across level ground with a 15-N force that is 34° above the horizontal. The work done is
a.
35 J
d.
3.9 ´ 102 J
b.
52 J
e.
2.1 ´ 103 J
c.
63 J
 

2. 
Which of the following is not a unit of energy?
a.
J
d.
W×s
b.
unit_2_review_files/i0030000.jpg
e.
unit_2_review_files/i0030001.jpg
c.
N×m
 

3. 
In which situation is work not done?
a.
a frozen turkey is carried upstairs
b.
a frozen turkey is carried on level ground
c.
a frozen turkey is dropped
d.
a frozen turkey is carried downstairs
e.
a frozen turkey is fired from a cannon
 

4. 
If the mass of a car is doubled and its speed is cut in half, then the kinetic energy changes by a factor of
a.
0.25
d.
2
b.
0.5
e.
4
c.
1
 

5. 
A bird flying at a height of 12 m doubles its speed as it descends to a height of 6.0 m. The gravitational potential energy has changed by a factor of
a.
0.25
d.
2
b.
0.5
e.
4
c.
1
 

6. 
A 5.0-kg cat travelling at 1.3 m/s [E] has a momentum of
a.
6.5 m/s [E]
d.
3.8 m/s [W]
b.
6.5 m/s [W]
e.
none of the above
c.
3.8 m/s [E]
 

7. 
A 55-kg person carrying a 5.0-kg ball slides along a horizontal frictionless surface. He tosses the ball perpendicular to his direction of travel relative to himself.
a.
His path will not change.
b.
The ball will have a smaller angle from the original path than he will.
c.
His speed does not change.
d.
He speeds up.
e.
He slows down.
 

8. 
Two objects of equal mass with the speeds indicated by the vectors below, collide and stick together.
unit_2_review_files/i0090000.jpg
Which vector below best represents the velocity of the combined objects after the collision?
unit_2_review_files/i0090001.jpg
a.
A
d.
D
b.
B
e.
E
c.
C
 

9. 
To compare the kinetic energies of two objects, you must know
a.
their masses
d.
the forces acting on them
b.
their velocities
e.
the work done to stop each of them
c.
their momenta
 

10. 
How far above the surface of Earth do you need to go for g to be reduced to 0.5 of its value on the surface of Earth?
a.
0.41rE
d.
1.4rE
b.
0.50rE
e.
2.0rE
c.
0.71rE
 

11. 
Earth’s mass is 5.98 ´ 1024 kg. Calculate the value of g at a point 4.8 ´ 105 km from the centre of Earth.
a.
9.8 ´ 10–2 N/kg
d.
1.7 ´ 103 N/kg
b.
8.3 ´ 105 N/kg
e.
9.8 ´ 10–5 N/kg
c.
1.7 ´ 10–3 N/kg
 

12. 
The average radius of orbit for Jupiter is 7.78 ´ 1011 m. Using CS = 3.355 ´ 1018 m3/s2, the period of orbit for Jupiter is
a.
4.25 ´ 102 s
d.
4.25 ´ 1012 s
b.
3.75 ´ 108 s
e.
1.80 ´ 105 s
c.
1.43 ´ 1021 s
 

13. 
A planet being orbited by a satellite collapses to half its original radius while maintaining the same mass. The period of orbit will increase by a factor of
a.
0.35
d.
2.0
b.
0.50
e.
2.8
c.
1.0
 

14. 
If the mass of Earth is 5.98 ´ 1024 kg and the radius is 6.38 ´ 106 m, the gravitational potential energy of a 1.2 ´ 103-kg satellite located in an orbit 230 km above the surface of Earth is
a.
–1.1 ´ 104 J
d.
–9.0 ´ 1012 J
b.
–7.2 ´ 1010 J
e.
–2.1 ´ 1015 J
c.
–2.1 ´ 1012 J
 

15. 
If an orbiting satellite has a total energy of –1.4 ´ 1012 J, then the binding energy is
a.
–1.4 ´ 1012 J
d.
–7.0 ´ 1011 J
b.
+1.4 ´ 1012 J
e.
not enough information
c.
–2.8 ´ 1012 J
 

Short Answer
 

16. 
Give an example of a common type of employment (or “work”) that does not involve a significant amount of the physical definition of work.
 

17. 
Why are speed limits reduced near most schools?
 

18. 
How is speed related to braking distance?
 

19. 
A 0.25-kg snowball moving at 15 m/s [E] collides and sticks with a 1.9-kg toy truck travelling at 2.8 m/s [W]. Neglecting friction, calculate the velocity of the snowball–truck system after the collision.
 

20. 
Why can we not have a satellite in orbit 15 km above Earth’s surface?
 

Problem
 

21. 
Two common and identical carts are used to perform an experiment. Cart A is pushed toward the stationary cart B with a velocity of 2.6 m/s. After the collision, cart A bounces back with a speed of 0.8 m/s and cart B moves of with a speed of 3.4 m/s. Why is this not possible?
 

22. 
During a game of billiards, the 0.30-kg cue ball, travelling at 2.1 m/s, glances off a stationary 0.28-kg billiard ball so that the billiard ball moves off at 1.4 m/s at an angle of 38º from the cue ball’s original path. Find the new speed of the cue ball.
 

23. 
Calculate the value of the gravitational field strength g, 250 km above the surface of Earth.
 

24. 
The average radius of orbit for Jupiter is 7.78 ´ 1011 m. Using CS = 3.355 ´ 1018 m3/s2, calculate the number of Earth years it will take for Jupiter to complete one orbit.
 

25. 
Mercury has a radius of 2.57 ´ 106 m and an escape speed of 4.13 km/s. What is the mass of Mercury?
 

26. 
What is the Schwartzschild radius of a black hole of mass 4.7 ´ 1034 kg?
 

Essay
 

27. 
Use your understanding of frictional forces, work, and kinetic energy to explain why it is common to have a reduced speed near an area with small children. Word your explanation so that it can be understood by someone who has never taken high school physics.
 

28. 
Safety during sporting events becomes increasingly important as people and machines get faster and push the limits of human accomplishment. Choose a sporting event and, referring to concepts covered in this unit, explain how safety equipment minimizes risk of injury and how it has affected the sport.
 



 
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