1. Physics 218: Mechanics Instructor: Dr. Tatiana Erukhimova Lecture 18

2. >80 >70>60>50>40>30 >80=A>70=B>55=C>38=D Average=62.4 Median = 66 High=95 Sec. 807 – 59.2 Sec. 808 – 67.8 Sec. 809 – 59.8

3. Momentum is a vector! Vector equation!

4. If

5. Conservation of Momentum If there is no external force on a system, then the total momentum of the system is a constant

6. True in X and Y directions separately!

7. Problem Solving For Conservation of Momentum problems: 1.BEFORE and AFTER 2.Do X and Y Separately

8. Before X Y

9. After Y X

10. Inelastic collision A collision in which the total kinetic energy after the collision is not equal to the kinetic energy before the collision is called an inelastic collision. A B BEFORE AFTER A B V after ?

11. Perfectly elastic collision A collision in which the total kinetic energy after the collision is the same than that before the collision is called an elastic collision. A B

12. A block of mass m is moving along x axis with a velocity of V 0. It collides with a block of mass M, initially at rest. 1) What is the change in kinetic energy of the system of two balls: a) if the collision is perfectly elastic; b) if the collision is perfectly inelastic (balls stick together after collision). 2) For m = M = m 0, find the velocity of each ball after a perfectly elastic collision. Quiz 1

13. Problem 2 from handout

14. Have a great day! Reading: Chapter 10 Hw: All Chapter 10 problems and exercises