\includegraphics{figure_4}

A truck of mass 1750 kg is towing a car of mass 750 kg along a straight horizontal road. The two vehicles are joined by a light towbar which is inclined at an angle $\theta$ to the road, as shown in Figure 4. The vehicles are travelling at 20 m s$^{-1}$ as they enter a zone where the speed limit is 14 m s$^{-1}$. The truck's brakes are applied to give a constant braking force on the truck. The distance travelled between the instant when the brakes are applied and the instant when the speed of each vehicle is 14 m s$^{-1}$ is 100 m.

\begin{enumerate}[label=(\alph*)]
\item Find the deceleration of the truck and the car. [3]
\end{enumerate}

The constant braking force on the truck has magnitude $R$ newtons. The truck and the car also experience constant resistances to motion of 500 N and 300 N respectively. Given that cos $\theta = 0.9$, find

\begin{enumerate}[label=(\alph*)]
\setcounter{enumi}{1}
\item the force in the towbar, [4]
\item the value of $R$. [4]
\end{enumerate}

\hfill \mbox{\textit{Edexcel M1 2013 Q7 [11]}}