## Physics: Principles with Applications (7th Edition)

The momentum in the horizontal direction will be conserved. Let the positive direction be the direction in which the boxcar was originally moving. $$(7700 kg)(14 m/s) + (M)(0 m/s) = (7700 kg + M)(5.0 m/s)$$ Solve for M=14000 kg, rounded to 2 significant figures.