1 A particle \(P\) is projected vertically downwards from a fixed point \(O\) with initial speed \(4.2 \mathrm {~ms} ^ { - 1 }\), and takes 1.5 s to reach the ground. Calculate
- the speed of \(P\) when it reaches the ground,
- the height of \(O\) above the ground,
- the speed of \(P\) when it is 5 m above the ground.