A railway truck \(S\) of mass 20 tonnes is moving along a straight horizontal track when it collides with another railway truck \(T\) of mass 30 tonnes which is at rest. Immediately before the collision the speed of \(S\) is \(4 \mathrm {~m} \mathrm {~s} ^ { - 1 }\)
As a result of the collision, the two railway trucks join together.
Find
the common speed of the railway trucks immediately after the collision,
the magnitude of the impulse exerted on \(S\) in the collision, stating the units of your answer.