6. A car pulls a trailer along a straight horizontal road using a light inextensible towbar. The mass of the car is $M \mathrm {~kg}$, the mass of the trailer is 600 kg and the towbar is horizontal and parallel to the direction of motion. There is a resistance to motion of magnitude 200 N acting on the car and a resistance to motion of magnitude 100 N acting on the trailer. The driver of the car spots a hazard ahead. Instantly he reduces the force produced by the engine of the car to zero and applies the brakes of the car. The brakes produce a braking force on the car of magnitude 6500 N and the car and the trailer have a constant deceleration of magnitude $4 \mathrm {~m} \mathrm {~s} ^ { - 2 }$

Given that the resistances to motion on the car and trailer are unchanged and that the car comes to rest after travelling 40.5 m from the point where the brakes were applied, find
\begin{enumerate}[label=(\alph*)]
\item the thrust in the towbar while the car is braking,
\item the value of $M$,
\item the time it takes for the car to stop after the brakes are applied.
\end{enumerate}

\hfill \mbox{\textit{Edexcel M1 2018 Q6 [9]}}