5. 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 \(3 \mathrm {~m} \mathrm {~s} ^ { - 1 }\), the speed of \(B\) is \(4 \mathrm {~m} \mathrm {~s} ^ { - 1 }\), 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.

1. Find the speed and direction of \(C\) after the collision.
2. Find, in Ns, the magnitude of the impulse exerted by \(B\) on \(A\) in the collision.
3. State a modelling assumption which you have made about the trucks in your solution 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.
4. Find the value of \(d\).
   (4)