7 A helicopter is initially hovering above a lighthouse. It then sets off so that its acceleration is $( 0.5 \mathbf { i } + 0.375 \mathbf { j } ) \mathrm { m } \mathrm { s } ^ { - 2 }$. The helicopter does not change its height above sea level as it moves. The unit vectors $\mathbf { i }$ and $\mathbf { j }$ are directed east and north respectively.
\begin{enumerate}[label=(\alph*)]
\item Find the speed of the helicopter 20 seconds after it leaves its position above the lighthouse.
\item Find the bearing on which the helicopter is travelling, giving your answer to the nearest degree.
\item The helicopter stops accelerating when it is 500 metres from its initial position.

Find the time that it takes for the helicopter to travel from its initial position to the point where it stops accelerating.
\end{enumerate}

\hfill \mbox{\textit{AQA M1 2011 Q7 [12]}}