5. Two particles \(P\) and \(Q\), of masses \(2 m\) and \(m\) respectively, are on a smooth horizontal table. Particle \(Q\) is at rest and particle \(P\) collides directly with it when moving with speed \(u\). After the collision the total kinetic energy of the two particles is \(\frac { 3 } { 4 } m u ^ { 2 }\). Find

1. the speed of \(Q\) immediately after the collision,
2. the coefficient of restitution between the particles.