5. At time \(t = 0\), a particle \(P\) is at the origin \(O\), moving with speed \(18 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) along the \(x\)-axis, in the positive \(x\)-direction. At time \(t\) seconds \(( t > 0 )\) the acceleration of \(P\) has magnitude \(\frac { 3 } { \sqrt { } ( t + 4 ) } \mathrm { m } \mathrm { s } ^ { - 2 }\) and is directed towards \(O\).

1. Show that, at time \(t\) seconds, the velocity of \(P\) is \([ 30 - 6 \sqrt { } ( t + 4 ) ] \mathrm { m } \mathrm { s } ^ { - 1 }\).
2. Find the distance of \(P\) from \(O\) when \(P\) comes to instantaneous rest.