Question

A railway wagon of mass 20t is moving along a level track at 10km/h when it collides and couples together with a second wagon of mass 25t moving in the

same direction at 5km/h. If the two wagons couple together after the impact, what would be their common velocity?

Answer 1

Using conservation of momentum, you have the total initial momentum in the system is wqual to the total final momentum in the system.

mv + mv = mv

plug in all the values

(20t)(10) + (25t)(5) = (45t)Vfinal

distribute everything

200t + 125t = 45t Vf

simplify

325t = 45t Vf

divide both sides by 45t

7.22 = Vf

So their final common velocity is 7.22km/h in the same direction as they were travelling before