## Lecture 9: Momentum Conservation

September 21, 2017

• Read: 9-2 thru 9-6 (stop at “Elastic Collisions in Two Dimensions” on p. 159)
• Study: Ex 9.5; Got It 9.4; Exs 9.7, 9.8

### Objectives

• (Continuing objective) Relate the concepts of relativity, momentum, and oscillations to “everyday” situations and discuss various applications of the concepts to practical problems in various fields of science, medicine and engineering.
• Calculate the vector momentum of various objects.
• State and recognize the conditions under which conservation of linear momentum applies.
• Apply conservation of linear momentum to various isolated systems, including explosions and collisions in one or two dimensions. For elastic collisions, be able to use both conservation of momentum and conservation of energy (or alternately the equivalence between speed of approach and speed of recession) to solve for unknowns.

### Homework

• Friday's Assigned Problems: A26, A27, A28; CH 9: 8, 20, 23, 29, 33, 53, 57

Answers: CH 9 #20 $-10.6 \hat\imath - 2.8 \hat\jmath \,\text{m/s}$.

• Monday's Hand-In Problems: A29, A74; CH 9: 28, 34, 52

### Videos of example problems

To see the problem statement, click on the link below. To play the video example, click on the underlined words "Video Demonstration" near the top of the page with the problem statement.
• Video Example #1: A worked out problem on elastic collisions: the bouncing superball demo from lecture. ans: 4 m/s, up
• Video Example #2: Another example of momentum conservation. ans: 1/3 (or 3, depending).