Chipola Junior College

PHY 2048C - General Physics

Momentum Practice Problems

1. A 50.5 kg quarterback is running with a football downfield at a speed of 2 m/s and is tackled by another player with a mass of 70 kg running toward him at 4 m/s. When the tackler grabs the quarterback, they both fall backward at the same speed of 1 m/s (opposite to the original direction of the quarterback). In the process, the 0.5 kg football comes loose at the moment the collision takes place.

a) Calculate the velocity of the fumbled football.

b) What is the impulse delivered to the quarterback? (Do not include the mass of the football).

c) If the impact of the tackle lasts for 0.1 second, then find the average force of the tackler on the quarterback.

d) Find the velocity of the center of mass of the quarterback-football-tackler system.

2. Consider a 20 kg ball sliding toward a stationary 15 kg block at 10 m/s. Answer the following questions assuming a frictionless surface.

a) Find the velocities of the block and the ball assuming an elastic collision.

b) What is the total kinetic energy of the system?

c) Calculate the force of impact between the two objects.

d) Find the center of mass velocity.

e) Calculate the kinetic energy associated with the relative motion of the masses.

3. Consider the action of shooting a tin can with a pellet gun. Assume the 0.01 kg pellets leave the gun with a velocity of 150 m/s.

a) If the pellet hits a 0.5 kg tin can, find the velocities of the can and pellet if they collide elastically.

b) Now consider the collision of the pellet and can in an inelastic collision. If the pellet stops after hitting the can, then find the velocity of the can just after the collision.

c) How much kinetic energy is lost in the inelastic collision of part b)?

4. Consider a 10 kg ball sliding toward a stationary 20 kg block at 30 m/s. Answer the following questions assuming a frictionless surface. Assume the collision lasts for 0.05 s.

a)Find the velocities of the block and the ball assuming an elastic collision.

b)Calculate the force of impact between the ball and block.

c) What is the total kinetic energy of the system?

5. Consider the frictionless horizontal table shown below shown below. A block of mass m₂=2 kg moves in the downward direction at 4 m/s and is shot by a 0.01 kg bullet initially travelling at 150 m/s in the x-direction. The bullet slows to 20 m/s after it passes out of the other side of the block in 0.05 seconds.

a) Find the final velocity of the block.

b) What is the force of contact between the block and the bullet?

c) Is the collision elastic or inelastic? Show your reasoning for full credit.

6. Armageddon. An asteroid of 5x10⁸ kg is heading toward the earth at a speed of 1500 m/s. It is your job to save the earth by using the technology available to you. Choose the positive x-axis as the initial direction of motion for the asteroid.

a)Your first try is to put a rocket which can sustain a thrust of 8x10⁵ N on the side of the asteroid nearest to the earth. Calculate the amount of time required to bring the asteroid to rest, so the rocket stops speeding toward the earth.

b)Realizing you do not have that long to wait before the earth is doomed, you send a team to the asteroid in hopes of blowing it up. After detonating your explosives, you notice the asteroid splits into a fragment m1=1x10⁸ kg and another piece m2=4x10⁸ kg which you measure has a velocity backward of v2=-1000 m/s i+ 500 m/s j. Find the velocity of the smaller fragment after the explosion.

c)How much energy was added to the system because of the explosion?