M1 January 2012 Q1

1. A railway truck \(P\), of mass \(m\) kg, is moving along a straight horizontal track with speed 15 m s\(^{-1}\). Truck \(P\) collides with a truck \(Q\) of mass 3000 kg, which is at rest on the same track. Immediately after the collision the speed of \(P\) is 3 m s\(^{-1}\) and the speed of \(Q\) is 9 m s\(^{-1}\). The direction of motion of \(P\) is reversed by the collision.

Modelling the trucks as particles, find