Question 1

A 3.0 kg ball is thrown horizontally at 4.0 m/s to a person standing on a 75 kg skateboard. The person catches the ball. What is the final speed of the person and skateboard (including the ball) after the catch?

Accepted Answer

$$0.15\ \mathrm{m/s}$$

Question 2

Which of the following best describes a perfectly inelastic collision?

Accepted Answer

The two objects stick together and move with a common final velocity.

Question 3

Bailey (mass $$26\ \mathrm{kg}) $$runs at $$4.0\ \mathrm{m/s}$$ and jumps onto a $$5.9\ \mathrm{kg}$$ sled at rest. What is the speed of the sled and Bailey just after she lands on it?

Accepted Answer

$$3.3\ \mathrm{m/s}$$

Question 4

Two boxes, one of mass $$1\ \mathrm{kg}$$ and the other $$2\ \mathrm{kg}$$, are at rest on a frictionless surface. An explosion pushes the $$1\ \mathrm{kg}$$ box to the left at $$4\ \mathrm{m/s}. $$What is the velocity of the $$2\ \mathrm{kg}$$ box after the explosion?

Accepted Answer

$$2\ \mathrm{m/s}$$\ to\ the\ right

Question 5

A $$30\ \mathrm{g}$$ ball is fired from a $$1.2\ \mathrm{kg}$$ toy rifle at $$15\ \mathrm{m/s}. $$What is the recoil speed of the rifle?

Accepted Answer

$$0.38\ \mathrm{m/s}$$

Question 6

A $$10\ \mathrm{g}$$ bullet is fired into a $$1.0\ \mathrm{kg}$$ wood block, where it lodges. The block and bullet slide $$4.0\ \mathrm{m}$$ across a floor with $$\mu_k = 0.20. $$What was the bullet's speed before impact?

Accepted Answer

$$400\ \mathrm{m/s}$$

Question 7

In a perfectly inelastic collision, which of the following is always true?

Accepted Answer

The two objects move together with a common velocity after the collision.

Question 8

Two railroad cars, one of mass $$2.0 	imes 10^4$\ \mathrm{kg}$$ moving at $$1.5\ \mathrm{m/s} to $$the right and another of mass $$4.0 	imes 10^4$\ \mathrm{kg}$$, couple and move together at $$-0.25\ \mathrm{m/s} (to $$the left). What was the initial velocity of the heavier car?

Accepted Answer

$$-1.1\ \mathrm{m/s}$$

Question 9

Which of the following statements about explosions is correct?

Accepted Answer

If the system is isolated, the total momentum is conserved during the explosion.

Question 10

A $$1\ \mathrm{kg}$$ box slides at $$4\ \mathrm{m/s} to $$the right and collides with a $$2\ \mathrm{kg}$$ box at rest on a frictionless surface. If the boxes stick together, what is their velocity after the collision?

Accepted Answer

$$1.3\ \mathrm{m/s}$$\ to\ the\ right

Question 11

A clay ball of mass $$0.2\ \mathrm{kg}$$ moving at $$5\ \mathrm{m/s}$$ hits and sticks to a stationary $$0.3\ \mathrm{kg}$$ block. What is their velocity after the collision?

Accepted Answer

$$2\ \mathrm{m/s}$$

Question 12

Which of the following is NOT a valid step in solving a conservation of momentum problem?

Accepted Answer

Assume external forces are significant during the interaction.

Question 13

A $$0.5\ \mathrm{kg}$$ ball moving at $$6\ \mathrm{m/s}$$ collides head-on and sticks to a $$1.5\ \mathrm{kg}$$ ball moving at $$-2\ \mathrm{m/s}. $$What is the final velocity of the combined mass?

Accepted Answer

$$0\ \mathrm{m/s}$$

Question 14

A $$2\ \mathrm{kg}$$ cart moving at $$3\ \mathrm{m/s}$$ collides elastically with a $$1\ \mathrm{kg}$$ cart at rest. What is the velocity of the $$2\ \mathrm{kg}$$ cart after the collision?

Accepted Answer

$$1\ \mathrm{m/s}$$

Question 15

A $$0.1\ \mathrm{kg}$$ ball is thrown at $$10\ \mathrm{m/s}$$ and embeds itself in a $$0.9\ \mathrm{kg}$$ block at rest. What is the velocity of the block and ball after the collision?

Accepted Answer

$$1\ \mathrm{m/s}$$

Question 16

Which of the following is a real-world example of a perfectly inelastic collision?

Accepted Answer

A bullet embedding itself in a block of wood.

Question 17

A $$5\ \mathrm{kg}$$ object moving at $$2\ \mathrm{m/s}$$ collides with a $$3\ \mathrm{kg}$$ object at rest. If they stick together, what is their final velocity?

Accepted Answer

$$1.25\ \mathrm{m/s}$$

Question 18

In the context of momentum conservation, which of the following is the best reason to choose a system that is isolated?

Accepted Answer

So that external forces can be ignored and momentum is conserved.

Question 19

A $$0.2\ \mathrm{kg}$$ ball moving at $$3\ \mathrm{m/s}$$ collides and sticks to a $$0.8\ \mathrm{kg}$$ block at rest. What is the final velocity of the combined mass?

Accepted Answer

$$0.6\ \mathrm{m/s}$$

Conservation of Momentum and Inelastic Collisions

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