1. 1. What is the difference in elastic and inelastic collisions?

2. Both types of collisions conserve momentum. (Momentum is conserved in all collisions.) Elastic collisions also conserve kinetic energy. Inelastic collisions do not conserve kinetic energy.

3. 2. A 5 gram bullet is fired at a speed of 1000 m/s. It collides with and lodges in a 2 kg block of wood. What is the speed of the bullet-wood block combination after the collision?

4. mv + mv = mv 0.005 x 1000 + 2 x 0 = 2.005 x v 5 = 2.005v v = 2.49 m/s

5. 3. What is the kinetic energy of the bullet- wood block system in question 2 before the collision?

6. KE = ½ mv 2 KE = ½ 0.005 x 1000 2 KE = 2500 J

7. 4. What is the kinetic energy of the bullet- wood block system in question 2 after the collision?

8. KE = ½ mv 2 KE = ½ 2.005 x 2.49 2 KE = 6.2 J

9. 5. Is the collision in question 2 elastic or inelastic?

10. KE drops from 2500 J to 6.2 J. The collision is inelastic. (perfectly inelastic)

11. 6. A 0.5 kg croquet ball moving 4 m/s collides with another 0.5 kg croquet ball which is at rest. The first ball stops after the collision. What is the velocity of the second ball after the collision?

12. mv + mv = mv + mv 0.5 x 4 + 0.5 x 0 = 0.5 x 0 + 0.5v 2 kgm/s = 0.5v v = 4 m/s

13. 7. What is the kinetic energy of the two croquet ball system in question 6 before the collision?

14. KE = ½ mv 2 KE = ½ 0.5 x 4 2 KE = 4 J

15. 8. What is the kinetic energy of the two croquet ball system in question 6 after the collision?

16. KE = ½ mv 2 KE = ½ 0.5 x 4 2 KE = 4 J

17. 9. Is the collision in question 6 elastic or inelastic?

18. KE before the collision = 4 J. KE after = 4 J. KE is conserved so it is an elastic collision.

19. 10. A 5 kg ball is moving right at a velocity of 6 m/s. It makes a head on collision with another 5 kg ball which is moving left at 4 m/s. After the collision, the first marble moves left at 4 m/s. What is the velocity of the second ball after the collision?

20. mv + mv = mv + mv 5 x 6 + 5 x -4 = 5 x -4 + 5v 30 + -20 = -20 + 5v v = 6 m/s

21. 11. What is the kinetic energy of the two ball system in question 10 before the collision?

22. KE = ½ mv 2 KE = ½ 5 x 6 2 + ½ 5 x -4 2 KE = 90 J + 40 J KE = 130 J

23. 12. What is the kinetic energy of the two ball system in question 10 after the collision?

24. KE = ½ mv 2 KE = ½ 5 x -4 2 + ½ 5 x 6 2 KE = 40 J + 90 J KE = 130 J

25. 13. Is the collision in question 10 elastic or inelastic?

26. KE before the collision = 130 J. KE after = 130 J. KE is conserved so it is an elastic collision.

27. 14. How do we identify perfectly inelastic collisions?

28. In a perfectly inelastic collision, the objects stick together and are treated as one object.