A 9500 boxcar traveling at 13.0 strikes a second boxcar at rest. The two stick together and move off with a speed of 4.5 . What is the mass of the second car?
The first time, the 9500 kg boxcar moving to the right at 13 m/s, and the second boxcar sitting still (assumed) on the tracks. The next time, the two boxcars with a total mass of 9500 kg + M, where M is the unknown mass of the second car, move at 4.5 m/s. The total momentum rests still:
9500 kg·13 m/s + 0 = (9500 kg + M)·(4.5 m/s) ==> M = 17944.(4) kg.