7. Two particles \(P\) and \(Q\), of masses 0.3 kg and 0.2 kg respectively, are moving towards each other along a straight line. \(P\) has speed \(4 \mathrm {~ms} ^ { - 1 }\). They collide directly. After the collision the direction of motion of both particles has been reversed, and \(Q\) has speed \(2 \mathrm {~ms} ^ { - 1 }\). The coefficient of restitution between \(P\) and \(Q\) is \(\frac { 1 } { 3 }\). Find

1. the speed of \(Q\) before the collision,
2. the speed of \(P\) after the collision,
3. the kinetic energy, in J , lost in the impact.