Question

A railroad diesel engine weighs four times as much as a freight car. If the diesel engine coasts at 24 km/h into a freight car that is at rest, how fast do the two coast after they couple?

Answer 1

Using conservation of momentum ..

Initial mom. of engine = (Mkg x 4 km/h) = 4M kg.km/h

Final (joined) mom. = (1.25Mkg x Vm/s) .. .. (joint mass = M + M/4)