PHY 2048C General Physics I with lab Spring 2011 CRNs 11154, & Dr. Derrick Boucher Assoc. Prof. of Physics Session 10, Chapter 9

Chapter 9 Homework Due midnight

Chapter 9 Practice Problems 11, 23, 25, 29, 31, 35, 39, 55 Unless otherwise indicated, all practice material is from the “Exercises and Problems” section at the end of the chapter. (Not “Questions.”)

Example, Problem 9-8, p. 262

Impulse and Momentum Momentum is the product of a particle’s mass and velocity, has units of kg m/s, and is given by The impulse upon a particle is defined as Impulse has units of N s, but you should be able to show that N s are equivalent to kg m/s. The impulse- momentum theorem is

EXAMPLE 9.2 A bouncing ball QUESTION:

EXAMPLE 9.2 A bouncing ball

Example, Problem 9-8, p. 262

Conservation of Momentum

Stated mathematically, the law of conservation of momentum for an isolated system is The total momentum after an interaction is equal to the total momentum before the interaction.

Example, Problem 9-18, p. 263

Conservation of Momentum Depends on the System

Problem-Solving Strategy: Conservation of Momentum TWO (or more) DIMENSIONS

Example, Problem (made-up)

Chapter 9. Clicker Questions

The cart’s change of momentum is A. 30 kg m/s. B. 10 kg m/s. C.–10 kg m/s. D.–20 kg m/s. E.–30 kg m/s.

A. They exert equal impulses because they have equal momenta. B. The clay ball exerts a larger impulse because it sticks. C. Neither exerts an impulse on the wall because the wall doesn’t move. D. The rubber ball exerts a larger impulse because it bounces. A 10 g rubber ball and a 10 g clay ball are thrown at a wall with equal speeds. The rubber ball bounces, the clay ball sticks. Which ball exerts a larger impulse on the wall?

Objects A and C are made of different materials, with different “springiness,” but they have the same mass and are initially at rest. When ball B collides with object A, the ball ends up at rest. When ball B is thrown with the same speed and collides with object C, the ball rebounds to the left. Compare the velocities of A and C after the collisions. Is v A greater than, equal to, or less than v C ? A. v A > v C B. v A < v C C. v A = v C

A. v f = v 2. B. v f is less than v 2. C. v f is greater than v 2, but less than v 1. D. v f = v 1. E. v f is greater than v 1. The two particles are both moving to the right. Particle 1 catches up with particle 2 and collides with it. The particles stick together and continue on with velocity v f. Which of these statements is true?

An explosion in a rigid pipe shoots out three pieces. A 6 g piece comes out the right end. A 4 g piece comes out the left end with twice the speed of the 6 g piece. From which end does the third piece emerge? A. Right end B. Left end