Lesson 3.03Conservation of Linear Momentum and Collisions
Self-Check Quiz
1. Momentum of a system is conserved only when:
a. there are no forces acting on the system
b. there are no external forces acting on the system
c. there are no internal forces acting on the system
d. the system is not moving
e. the system has been moving long enough to gain momentum
Answer: _____
2. An elephant is hit by a ping pong ball. The magnitude of the change in momentum is
a. greatest for the elephant
b. greatest for the ping pong ball
c. the same for both
d. depends on the ratio of the masses of the ball and elephant
e. none of these
Answer: _____
3. A 1000 kg car traveling east at 20 m/s collides head-on with a 1500 kg car traveling west at 10 m/s. The cars stick together after the collision. What is their common velocity after the collision?
a. 3 m/s east
b. 4 m/s east
c. 6 m/s west
d. 14 m/s east
e. none of these
Answer: _____
4. Which of the following is a correct statement of the law of conservation of momentum?
a. The rate of change of momentum of a body is equal to the net force applied to it.
b. The total momentum of an isolated system of bodies remains constant.
c. The total momentum is always conserved.
d. The sum of the impulses momenta of the objects in an isolated system is always conserved.
e. None of these.
Answer: _____
5. A large platform is initially at rest on a smooth surface. A dog on the platform starts running toward the east. The mass of the dog is one-half the mass of the platform. When the dog moves toward the east with a speed vo, the platform moves toward the ______with a speed ______.
a. east ... vo/2
b. east ... 2 vo
c. west ... vo/2
d. west ... 2 vo
e. none of these
Answer: _____
6. A 0.240 kg glider moving with a velocity of 0.600 m/s collides head-on with a 0.260 kg glider moving along the same line in the opposite direction with a velocity of 0.200 m/s. The collision is perfectly inelastic. The final velocity of the combined gliders is _____ m/s.
a. 0.563
b. 0.184
c. 0.0484
d. -0.392
e. none of these
Answer: _____
7. A 20,000 kg car moving with a speed of 4.00 m/s collides with a 50,000 kg car moving with a speed of 1.80 m/s in the same direction. Find the speed of the combined cars after the collision which is perfectly inelastic.
a. 1.60 m/s
b. 2.43 m/s
c. 2.00 m/s
d. 1.57 m/s
e. none of these
Answer: _____
8. A 40 kg boy dives horizontally off a 600 kg raft. If the boy's speed at the moment he is leaving the raft is 4 m/s, what is the raft's speed?
a. 0.2 m/s
b. 0.56 m/s
c. 0.6 m/s
d. 4 m/s
e. none of these
Answer: _____
9. A cannonball explodes into several fragments in mid-air. The total momentum of the fragments after this explosion:
a. is the same as the momentum of the cannonball immediately before the explosion
b. has been changed into the kinetic energy of the fragments
c. is less than the momentum of the cannonball immediately before the explosion
d. is more than the momentum of the cannonball immediately before the explosion
e. has been changed into radiant energy
Answer: _____
10. In an inelastic collision:
a. momentum is conserved, but not kinetic energy.
b. kinetic energy is conserved, but not momentum.
c. both momentum and kinetic energy are conserved.
d. neither momentum nor kinetic energy are conserved.
Answer: _____
11. A 20,000 kg car moving with a speed of 4.00 m/s collides with a 50,000 kg truck moving with a speed of 1.80 m/s in the same direction. The change in kinetic energy of the truck is _____ J.
a. 160000
b. -34000
c. -101000
d. -207000
e. none of these
Answer: _____
12. The linear momentum of a bullet-gun system is zero before the gun fires. Afterwards:
a. the kinetic energy is zero
b. the momentum is zero
c. both A and B
d. neither A or B
Answer: _____
13. Blocks A and B are moving toward each other along the x axis. A has a mass of 2.0 kg and a velocity of 50 m/s, while B has a mass of 4.0 kg and a velocity of -25 m/s. They collide head-on and stick together. After the collision the velocities of A and B, respectively, are:
a. -50 and 25 m/s
b. 50 and -25 m/s
c. -25 and 50 m/s
d. 25 and -50 m/s
e. -25 and -50 m/s
Answer: _____
14. A 15,000 kg railroad freight car is coasting at a speed of 2 m/s. It collides and couples with another car with a mass of 50,000 kg, which was initially not moving. What percentage of the initial kinetic energy of the system is preserved after collision?
a. 14%
b. 23%
c. 86%
d. 100%
e. none of these
Answer: _____
15. A ballistic pendulum is a device used to measure the speed of a bullet. A bullet is fired at a block of wood hanging from two strings. The bullet embeds itself in the block and causes the combined block plus bullet system to swing up.
If the bullet is fired at 530 m/s and its mass is 65 g, what is the speed of the block with embedded bullet after collision? The mass of the block is 2.2 kg.
a. 12 m/s
b. 14 m/s
c. 16 m/s
d. 53 m/s
e. none of these
Answer: _____
16. How high will the pendulum & bullet rise in the above problem? (g = 9.8 m/s2)
a. 14 cm
b. 74 cm
c. 12.5 cm
d. 16.4 cm
e. none of these
Answer: _____