4 A particle \(P\) moves in a straight line starting from a point \(O\). At time \(t \mathrm {~s}\) after leaving \(O\), the displacement \(s \mathrm {~m}\) from \(O\) is given by \(s = t ^ { 3 } - 4 t ^ { 2 } + 4 t\) and the velocity is \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\).

1. Find an expression for \(v\) in terms of \(t\).
2. Find the two values of \(t\) for which \(P\) is at instantaneous rest.
3. Find the minimum velocity of \(P\).