1. Alice and Bob are of equal mass (60kg). Alice has a momentum of 60 kg*m/s. Bob is at rest. Alice runs into Bob and stops, while Bob starts moving.

a. What is Alice's momentum after the collision?

b. What is Bob's momentum after the collision?

c. How fast is Bob's moving after the collision?

2. Impact: A car of mass 1100kg moves at 24 m/s. What is the braking force needed to bring the car to a halt in 2.0 seconds?

3. Impact: What is the force on a 0.025 kg egg from a bed sheet as the egg hits the sheet at 4.0 m/s and takes 0.2 seconds to stop?

4. Explosion: A 8.0 kg shell leaves a 2.0 x 103 kg cannon, at a speed of 4.0 x 102 m/s. What is the recoil speed of the cannon?

5. Collision: A 1.0 kg dart moving horizontally at 10.0 m/s makes impact and sticks to a piece of wood with a mass of 9.0 kg, which then slides across a friction-free surface. What is the speed of the wood and dart after the collision?

6. Collision: A 10,000-kg train coasting at 10 m/s collides with a 2000-kg automobile coasting at 30 m/s in the opposite direction. If they stick together after the impact how fast and in what direction will they be moving?

Practice Activity B

Directions: Express your understanding of the concept and mathematics of momentum conservation by answering the following questions. Assume isolated systems and momentum conservation for each problem.

1. A 0.105-kg hockey puck moving at 48 m/s is caught by a 75-kg goalie at rest. With what velocity does the goalie slide on the ice after catching the puck?

2. A 35.0-g bullet strikes a 5.0-kg stationary wooden block and embeds itself in the block. The block and bullet move together at 8.6 m/s. What was the original velocity of the bullet? (CAUTION: Be careful of the units on velocity.)

3. A 35.0-g bullet moving at 475 m/s strikes a 2.5-kg wooden block. The bullet passes through the block, leaving at 275 m/s. The block was at rest when it was hit. How fast is it moving when the bullet leaves? (CAUTION: Be careful of the units on velocity.)

4. A 0.50-kg ball traveling at 6.0 m/s collides head-on with a 1.00-kg ball moving in the opposite direction at a velocity of -12.0 m/s. The 0.50-kg ball moves away at -14 m/s after the collision. Find the velocity of the second ball.

5. A 3000-kg truck moving rightward with a speed of 5 km/hr collides head-on with a 1000-kg car moving leftward with a speed of 10 km/hr. The two vehicles stick together and move with the same velocity after the collision. Determine the post-collision velocity of the car and truck. (CAREFUL: Be cautious of the +/- sign on the velocity of the two vehicles.)

6. During a goal-line stand, a 75-kg fullback moving eastward with a speed of 8 m/s collides head-on with a 100-kg lineman moving westward with a speed of 4 m/s. The two players collide and stick together, moving at the same velocity after the collision. Determine the the post-collision velocity of the two players. (CAREFUL: Be cautious of the +/- sign on the velocity of the two players.)

Practice Activity C

Directions: Express your understanding of the concept and mathematics of momentum by answering the following questions.

1. When fighting fires, a firefighter must use great caution to hold a hose that emits large amounts of water at high speeds. Why would such a task be difficult?

2. A large truck and a Volkswagen have a head-on collision.

3. Miles Tugo and Ben Travlun are riding in a bus at highway speed on a nice summer day when an unlucky bug splatters onto the windshield. Miles and Ben begin discussing the physics of the situation. Miles suggests that the momentum change of the bug is much greater than that of the bus. After all, argues Miles, there was no noticeable change in the speed of the bus compared to the obvious change in the speed of the bug. Ben disagrees entirely, arguing that both bug and bus encounter the same force, momentum change, and impulse. Who do you agree with? Support your answer.

4. If a ball is projected upward from the ground with ten units of momentum, what is the momentum of recoil of the Earth? ____________ Do we feel this? Explain.

5. If a 5-kg bowling ball is projected upward with a velocity of 2.0 m/s, then what is the recoil velocity of the Earth (mass = 6.0 x 1024 kg).

6. A 120 kg lineman moving west at 2 m/s tackles an 80 kg football fullback moving east at 8 m/s. After the collision, both players move east at 2 m/s. Draw a vector diagram in which the before- and after-collision momenta of each player is represented by a momentum vector. Label the magnitude of each momentum vector.

7. In an effort to exact the most severe capital punishment upon a rather unpopular prisoner, the execution team at the Dark Ages Penitentiary searches for a bullet that is ten times as massive as the rifle itself. What type of individual would want to fire a rifle that holds a bullet that is ten times more massive than the rifle? Explain.

8. A baseball player holds a bat loosely and bunts a ball. Express your understanding of momentum conservation by filling in the tables below.

9. A Tomahawk cruise missile is launched from the barrel of a mobile missile launcher. Neglect friction. Express your understanding of momentum conservation by filling in the tables below.

a. Which vehicle experiences the greatest force of impact?

b. Which vehicle experiences the greatest impulse?

c. Which vehicle experiences the greatest momentum change?

d. Which vehicle experiences the greatest acceleration?

Review

Directions: Answer each of the following questions.

1. Babe Ruth swings with 200 N of force strikes a 1.5 kg ball for .05 seconds. How fast does the ball fly away if the pitch was moving at 16 m/s?

2. A .2 kg soccer ball moving at 10 m/s strikes a .1 kg plant. After the collision, the plant moves forward at 20 m/s. What happens to the ball?

3. Paul Simon shoots a .2 kg puck at 25 m/s and Patrick Roy catches the puck for .3 seconds. How much force does Patrick Roy absorb?

4. A 20-kilogram mass moving at a speed of 3.0 meters per second is stopped by a constant force of 15 newtons. How many seconds must the force act on the mass to stop it?

5. Chris Drury (85 kg) skating west at 8 m/s collides with Rob Ray (90 kg) who is skating east at 6 m/s. The two hockey players stick together and fall to the ice. What is their velocity after the collision?

6. If a 54 Ns impulse (recall, impulse is force*time, so it is measured in Newtons*seconds) is given to a 6-kg object, then the transfer of momentum is ____________.

7. Applying a force for a longer time increases the change in _________.

8. A 200 kg cannon fires a 5 kg cannonball at 40 m/s. How fast does the cannon recoil?

9. A 2 kg bowling ball moving at 6 m/s strikes a 1 kg pin. After the collision, the pin moves forward at 10 m/s. What happens to the ball?

10. An object's momentum can be calculated by multiplying the velocity of the object by its _____.

11. Which object has the least momentum?

A. Object C: m = 0.5 kg, v = 1000 m/s

B. Object E: m = 11 kg, v = 4 m/s

C. Object B: m = 10 kg, v = 12 m/s

D. Object A: m = 1 kg, v = 100 m/s

E. Object D: m = 100

12. Bobby Orr takes a slapshot with a velocity of 38 m/s. He hits the .2 kg puck for .4 seconds. How much force does he use?

13. A firecracker is placed in the midst of a motionless cluster of billiard balls on a table. When the firecracker explodes, the balls scatter in all directions. The total momentum of the balls immediately after the explosion is (less than, greater than, equal to, or impossible to tell) than before the explosion.

14. When a golf club hits a golf ball, the change in momentum of the club is (less than, greater than, or equal to) the change in momentum of the ball.

15. Which block would require the smallest applied force to keep it moving at constant velocity?