5 Particles \(P\) and \(Q\) are projected vertically upwards, from different points on horizontal ground, with velocities of \(20 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) and \(25 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) respectively. \(Q\) is projected 0.4 s later than \(P\). Find

1. the time for which \(P\) 's height above the ground is greater than 15 m ,
2. the velocities of \(P\) and \(Q\) at the instant when the particles are at the same height.