3 A particle \(P\) of mass 0.3 kg is projected horizontally with speed \(u \mathrm {~ms} ^ { - 1 }\) from a fixed point \(O\) on a smooth horizontal surface. At time \(t \mathrm {~s}\) after projection \(P\) is \(x \mathrm {~m}\) from \(O\) and is moving with speed \(v \mathrm {~ms} ^ { - 1 }\). There is a force of magnitude \(1.2 v ^ { 3 } \mathrm {~N}\) resisting the motion of \(P\).

1. Find an expression for \(\frac { \mathrm { d } v } { \mathrm {~d} x }\) in terms of \(v\) and hence show that \(v = \frac { u } { 4 u x + 1 }\).
2. Given that \(x = 2\) when \(t = 9\) find the value of \(u\).