A railroad freight car with a mass of 29,000 kg is moving at 2.2 m/s when it runs into another car with a mass of 30,000 kg the second car is at rest the cars locked together what is the final velocity

This is very important!

Collision always conserves linear momentum:

m*v, ok?

So, beginning:

29,000*2.2

End:

59,000*v, because they go together (same speed)

v = 29,000*2.2/59,000 = 29*2.2/59 = 1.08 m/s

Remember it, it will come many times!