10 A particle P of mass 2 kg is projected vertically upwards from horizontal ground with an initial speed of \(14 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). At the same instant a particle \(Q\) of mass 8 kg is released from rest 5 m vertically above P . During the subsequent motion P and Q collide. The coefficient of restitution between P and Q is \(\frac { 11 } { 14 }\). Determine the time between this collision and P subsequently hitting the ground.