Here is my revision question. I dont know where to start. Can someone please show me how to do this?
Welcome to MHF, jonnyl!
A system of the form $\displaystyle \ddot x = g(\dot x, x, t)$ can be rewritten with $\displaystyle x_1=x$ and $\displaystyle x_2=\dot x$.
From this you get the system $\displaystyle \left[ \begin{array}{lll}\dot x_1 &=& x_2 \\ \dot x_2 &=& g(x_2, x_1, t) \end{array} \right.$