5 A particle \(P\) moves along the \(x\)-axis in the positive direction. The velocity of \(P\) at time \(t \mathrm {~s}\) is \(0.03 t ^ { 2 } \mathrm {~m} \mathrm {~s} ^ { - 1 }\). When \(t = 5\) the displacement of \(P\) from the origin \(O\) is 2.5 m .

1. Find an expression, in terms of \(t\), for the displacement of \(P\) from \(O\).
2. Find the velocity of \(P\) when its displacement from \(O\) is 11.25 m .