Car A of mass 1 000 kg,stationary at a traffic light,is hit from behind by car B of mass 1 200 kg,traveling at 18 m.s-1. Immediately after the collision car A moves forward at 12 m.s-1.

1. Assume that linear momentum is conserved during this collision. Calculate the speed of car B immediately after the collision.
2. Modern cars are designed to crumple partially on impact. Explain why the assumption made in the first question may not be valid in this case.

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