Section 9.2
Conservation of Momentum
Practice Test
1.
Two freight cars, each with a mass of 2.5×10
4
kg collide. One was initially moving at 3.7 m/s; the other was at rest. They stick together. What is their final speed?
a.
3.7 m/s
b.
0.54 m/s
c.
2.4 m/s
d.
1.9 m/s
Hint
2.
A 2.00-kg ball, A, is moving at a speed of 5.00 m/s. It collides with a stationary ball, B, of the same mass. After the collision, A moves off in a direction 30.0° to the left of its original direction. Ball B moves off in a direction 90.0° to the right of ball A's final direction. How fast is ball B moving after the collision?
a.
2.50 m/s
b.
8.66 m/s
c.
6.83 m/s
d.
5.00 m/s
Hint
3.
In Figure 9-6, if
v
C
is 1 m/s,
v
D
is 7 m/s, and the mass of each ball is 2 kg, how would the magnitudes of the forces exerted by each ball on the other during the collision compare?
a.
The magnitude of the force of D on C would be greater than the magnitude of the force of C on D.
b.
The magnitude of the force of C on D would be greater than the magnitude of the force of D on C.
c.
The magnitudes of the forces would be equal.
d.
They do not exert forces on each other.
Hint
4.
A 2.00-kg ball, A, is moving at a speed of 5.00 m/s. It collides with a stationary ball, B, of the same mass. After the collision, A moves off in a direction 30.0° to the left of its original direction. Ball B moves off in a direction 90.0° to the right of ball A's final direction. How fast is ball A moving after the collision?
a.
6.83 m/s
b.
4.33 m/s
c.
2.50 m/s
d.
8.66 m/s
Hint
5.
When the net external force on a closed system is zero, it is described as __________.
a.
non-accelerating
b.
a normal system
c.
motionless
d.
an isolated system
Hint
6.
In Figure 9-6, if
m
C
is 1 kg,
m
D
is100 kg, and the initial velocities of both balls are 5 m/s, how would the magnitudes of the forces exerted by each ball on the other during the collision compare?
a.
The magnitudes of the forces would be equal.
b.
They do not exert forces on each other.
c.
The magnitude of the force of C on D would be greater than the magnitude of the force of D on C.
d.
The magnitude of the force of D on C would be greater than the magnitude of the force of C on D.
Hint
7.
Two campers dock a canoe. One camper has a mass of 100.0 kg and moves forward at 3.0 m/s as he leaves the canoe to step onto the dock. With what speed do the canoe and other camper move if their combined mass is 175.0 kg?
a.
5.3 m/s
b.
4.0 m/s
c.
8.25 m/s
d.
1.7 m/s
Hint
8.
A 4.75-g bullet is fired with a velocity of 120.0 m/s toward a 20.0-kg stationary solid block resting on a frictionless surface. What is the change in momentum of the bullet if it is embedded in the block?
a.
-1.20×10
3
kg·m/s
b.
5.7 kg·m/s
c.
1.20×10
3
kg·m/s
d.
-0.57 kg·m/s
Hint
9.
The law of conservation of momentum states that __________.
a.
the momentum of any closed system with no net external force does not change
b.
momentum is neither created nor destroyed
c.
the momentum of any closed system does not change
d.
the momentum of any system does not change
Hint
10.
All the forces within a closed system are __________.
a.
angular forces
b.
external forces
c.
due to gravity
d.
internal forces
Hint
11.
Before a collision, a 50.0-kg object is moving at +5.0 m/s. Find the impulse that acted on the object if, after the collision, it moves at +8.0 m/s.
a.
4.5 kg[dot]m/s
b.
-4.5 kg[dot]m/s
c.
1.5×10
2
kg[dot]m/s
d.
-1.5×10
2
kg[dot]m/s
Hint
12.
Before a collision, a 35-kg object is moving at +10.0 m/s. Find the impulse that acted on the object if, after the collision, it moves at +8.0 m/s.
a.
-2.8×10
2
kg·m/s
b.
-7.0×10
1
kg·m/s
c.
7.0×10
1
kg·m/s
d.
-7.0×10
2
kg·m/s
Hint
13.
A system that doesn't gain or lose mass is said to be __________.
a.
isolated
b.
a closed system
c.
an internal system
d.
inert
Hint
