A truck of mass 3 tonnes moves on straight horizontal rails. It collides with truck $B$ of mass 1 tonne, which is moving on the same rails. Immediately before the collision, the speed of $A$ is $3 \text{ m s}^{-1}$, the speed of $B$ is $4 \text{ m s}^{-1}$, and the trucks are moving towards each other. In the collision, the trucks couple to form a single body $C$, which continues to move on the rails.

\begin{enumerate}[label=(\alph*)]
\item Find the speed and direction of $C$ after the collision. [4]
\item Find, in Ns, the magnitude of the impulse exerted by $B$ on $A$ in the collision. [3]
\item State a modelling assumption which you have made about the trucks in your solution [1]
\end{enumerate}

Immediately after the collision, a constant braking force of magnitude 250 N is applied to $C$. It comes to rest in a distance $d$ metres.

\begin{enumerate}[label=(\alph*)]
\setcounter{enumi}{3}
\item Find the value of $d$. [4]
\end{enumerate}

\hfill \mbox{\textit{Edexcel M1  Q5 [12]}}