1. A particle $P$ has mass 8 kg and a particle $Q$ has mass 5 kg. $P$ is moving towards $Q$ in a straight line on a smooth horizontal surface. The particles collide directly.

Immediately before the collision the speed of $P$ is 3 m s^-1 and $Q$ is at rest.

Immediately after the collision $P$ is travelling in the same direction with speed 1 m s^-1.

Use the principle of conservation of linear momentum to find the speed of $Q$ immediately after the collision.