A railroad diesel engine weighs four times as much as a freight car. The diesel engine coasts at 5 km/h into a freight car that is initially at rest. Use the conservation of momentum to show that after they couple together, the engine + car coast at 4 km/h.

Please show work step by step

Explanation:

Conservation of momentum :

Where :

= masses of object collided

= initial velocity before collision

= final velocity after collision

We have :

Mass of an engine =

Mass of an car=

Initial velocity of railroad engine

Initial velocity of car (rest)

Final velocity of  railroad engine (same direction )

Final velocity of car (same direction)

v = 4 km/h

The speed of the engine and car after they coupled together is 4 km/h.