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## Collisions

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**“before”**m2 m1 “after” m2 m1 “before” M “after” m2 m1 Collisions Procedure • Draw “before”, “after” • Define system so that Fext = 0 • Set up axes • Compute Ptotal “before” • Compute Ptotal “after” • Set them equal to each other Explosions**CORRECT**Chapter 7. Example 4 A railroad car is coasting along a horizontal track with speed V when it runs into and connects with a second identical railroad car, initially at rest. Assuming there is no friction between the cars and the rails, what is the speed of the two coupled cars after the collision? 1. V 2. V/2 3. V/4 4. 0 Work out Demo with gliders**CORRECT**Chapter 7. Example 4. What physical quantities are conserved in the above collision? 1. Only momentum is conserved2. Only total mechanical energy is conserved 3. Both are conserved4. Neither are conserved Momentum is conserved because the sum of external forces equal to zero. Total mechanical energy is not conserved because some of the energy is lost when the car runs into the other car.**CORRECT**Chapter 7. Example 5 Is it possible for a system of two objects to have zero total momentum and zero total kinetic energy after colliding, if both objects were moving before the collision? 1. YES 2. NO if both objects are moving in oposite directions with the same mass and velocity they would have a resulting velocity of zero. Demo with gliders