3 Three particles \(P , Q\) and \(R\), of masses \(0.1 \mathrm {~kg} , 0.2 \mathrm {~kg}\) and 0.5 kg respectively, are at rest in a straight line on a smooth horizontal plane. Particle \(P\) is projected towards \(Q\) at a speed of \(5 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). After \(P\) and \(Q\) collide, \(P\) rebounds with speed \(1 \mathrm {~ms} ^ { - 1 }\).

1. Find the speed of \(Q\) immediately after the collision with \(P\).
   \(Q\) now collides with \(R\). Immediately after the collision with \(Q , R\) begins to move with speed \(V \mathrm {~m} \mathrm {~s} ^ { - 1 }\).
2. Given that there is no subsequent collision between \(P\) and \(Q\), find the greatest possible value of \(V\).