Greatest distance of a particle from the origin and its acceleration when it first changes direction

A particle moves in a straight line. Its displacement from a fixed point \(\mathrm{O}\) at time \(t\) seconds is \(s\) centimetres, where \(s(t)=t^2\sin{t}+3t\cos{t}\), for \(0\leq t\leq6\).

1. Find the greatest distance between the particle and \(\mathrm{O}\).[3]
2. Find the acceleration of the particle at the moment when it changes direction for the first time.[4]