4 A particle \(P\) moving in a straight line has velocity \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\) at time \(t \mathrm {~s}\) after passing through a fixed point \(O\). It is given that \(v = 3.2 - 0.2 t ^ { 2 }\) for \(0 \leqslant t \leqslant 5\). Calculate
- the value of \(t\) when \(P\) is at instantaneous rest,
- the acceleration of \(P\) when it is at instantaneous rest,
- the greatest distance of \(P\) from \(O\).