1. C ONSERVATION OF M OMENTUM

2. B ELL R INGER  What is the impulse of a 10 kg sledge hammer hitting a solid brick wall if it is initially moving at 20 m/s and does not even shake the wall?

3. O BJECTIVES  What is conservation of momentum?  What is the equation for conservation of momentum?

4. C ONSERVATION OF M OMENTUM  When a collision occurs in an isolated system, the total momentum of the system does not change with the passage of time.

5. C ONSERVATION OF M OMENTUM  This means that the momentum of the system before is equal to the momentum of the system after.  Both in magnitude and direction.

6. C ONSERVATION OF M OMENTUM  Individual momentum may change, but total momentum is conserved!

7. C ONSERVATION OF M OMENTUM  Represented by: m 1 v 1 + m 2 v 2 = m 1 v 1 + m 2 v 2

8. C ONSERVATION OF M OMENTUM  This is true when no net external force acts on a system.

9. E XAMPLE  An archer stands at rest on frictionless ice and fires a 0.500 kg arrow horizontally at 50 m/s. The mass of the archer and the bow is 60.0 kg. With what velocity does the archer move across the ice after firing the arrow?

10. E XAMPLE  A 10 gram bullet is fired into a stationary block of wood m = 5 kg. The relative motion of the bullet stops inside the block. The speed of the bullet plus wood combination immediately after the collision is measured as 0.6 m/s. What was the original speed of the bullet?

11. E XAMPLE  A 45 kg girl is standing on a plank that has a mass of 150 kg. The plank, originally at rest, is free to slide on a frozen lake, which is flat and frictionless. The girl begins to walk along the plank at a constant speed of 1.5 m/s relative to the plank.

12. C ONTINUED What is the speed of the plank relative to the ice surface?