A truck \(P\) of mass \(2 M\) is moving with speed \(U\) on smooth straight horizontal rails. It collides directly with another truck \(Q\) of mass \(3 M\) which is moving with speed \(4 U\) in the opposite direction on the same rails. The trucks join so that immediately after the collision they move together. By modelling the trucks as particles, find
the speed of the trucks immediately after the collision,
the magnitude of the impulse exerted on \(P\) by \(Q\) in the collision.