Impulse and Momentum Study Guide

Hon Lab Physics

Chapter 6

  • What are impulse and momentum?
  • What is the Impulse-Momentum Theorem?
  • Be able to solve problems using the theorem.
  • Be able to answer conceptual questions.
  • Why does an egg thrown against a wall break but not a sheet?
  • Why are baseball players told to follow through?
  • In terms of force and time of impact, why is it safe for cars to have a crumple zone? Why is it safer for a dropped egg to have a crumple zone?
  • What is the Law of Conservation of Momentum?
  • Know how to solve problems using the Law of Conservation of Momentum.
  • What is the difference between an elastic collision, recoil, and perfectly inelastic collision? In which type(s) of situation(s) in kinetic energy conserved?
  • Know how to solve problems involving elastic collision, perfectly inelastic collisions, and recoil. Be able to solve for the change in kinetic energy (this includes verifying that the kinetic energy is conserved).
  • Be able to solve for 2 unknowns in an elastic collision.
  • Be able to incorporate previous concepts (such as energy) into multiple part collision problems.

Equations given on the test:

p = mvimpulse = Ft KE = ½mv2 PE = mgh PE=1/2 kx2 Ff = FN

v1i + v1f = v2i + v2f

You may use kinematic equations where necessary.

1. A 3.00 kg mud ball has a perfectly inelastic collision with a second mud ball that is initially at rest. The composite system moves with a speed equal to one third the original speed of the 3.00 kg mud ball. What is the mass of the second mud ball?(Ans: 6kg)

2. A1550 kg car moving south at 10.0 m/s collides with a 2550 kg car moving north. The cars stick together and move as a unit after the collision at a velocity of 5.22 m/s to the north. Find the velocity

of the 2550 kg car before the collision.(Ans: 14.5m/s N) How much energy is lost during the collision?

3. A 0.400 kg bead slides on a straight frictionless wire with a velocity of 3.50 cm/s to the right. The bead collides elastically with a larger 0.600 kg bead initially at rest. After the collision, the smaller bead moves to the left with a velocity of 0.70 cm/s. Find the distance the larger bead moves along the wire in the first 5.0 s following the collision.(Ans: 14cm)

4. A 0.15 kg baseball moving at +26 m/s is slowed to a stop by a catcher who exerts a constant force of -390 N.
a. What is the change in momentum of the ball? (Ans: -3.9kg m/s)

b. How long does it take this force to stop the ball? (0.01s)

5. A 0.4kg hockey puck moving at 48 m/s is caught by a 40-kg goalie at rest.

a. What type of interaction is this?

b. With what velocity does the goalie slide on the ice after catching the puck? (Ans: 0.475 m/s)

c. What is the decrease in kinetic energy of the puck? (Ans: approximately 460 J)

d. How much work was done on the puck by the goalie? (Ans:-460 J)

6. A stationary 80 kg man on ice skates throws a 0.2 kg baseball horizontally with a velocity of 30 m/s. What type of interaction is this? With what velocity will the man move after the throw?

(ANS: - 0.075 m/s)

7. Two balls are moving towards each other. Ball A has a mass of 0.75 kg, and is moving with a speed of 7 m/s. Ball B has a mass of 0.25 kg and is moving at 5.5 m/s in the other direction. The two balls collide head-on elastically. What are the final velocities of each ball? (ANS: 13.25m/s, 0.75m/s) Verify your answers by confirming that kinetic energy is conserved.
8. Larzan (Tarzan’s evil twin), whose mass is 95 kg, swings from a 4.2 m vine that is horizontal when he starts. At the bottom of his swing he picks up 65kg Jane in a perfectly inelastic collision. What is the height of the highest tree limb they can reach on their upward swing? (Ans: 1.48 m)

9. A 10kg boxsliding across the floor is slowed down uniformly from an initial velocity of 2m/s by friction. The coefficient of friction between the box and floor is 0.306.

a. What is the box’s velocity after 0.3s? (Ans: 1.1m/s) Do not use kinematic equations to solve part a.

b. How far does the car move during the 0.3s? (Ans: 0.33m)

c. How long does it take the box to come to a complete stop? (Ans: 0.67s)