2. Initial momentum of entire system is zero (neither object has KE – neither is moving)

3. The interaction between the two objects must be equal and opposite Note the velocity vectors – why does the cannonball have a greater magnitude of velocity than the cannon?

4. When the astronaut throws the ball, she goes in the opposite direction

5. 0 = m 1 v 1f + m 2 v 2f

6. A 2 kg rocket zooms upward at 5 m/s. It is propelled by 1 kg of water shooting downward. How fast does the water shoot out? Momentum Rocket = Momentum Exhaust Momentum Rocket = Momentum Exhaust 0 = m 1 v 1f + m 2 v 2f 0 = (2 kg)(5 m/s) + (1 kg)v 2f