## Physics (10th Edition)

Because there is no external force acting on the system, total vertical momentum is conserved, so $$p_{01, y}+p_{02, y}=p_{f1, y}+p_{f2, y}$$ We have $p_{01, y}=p_{02, y}=0$ and $p_{f1, y}=-5kg.m/s$ Therefore, $p_{f2, y}=5kg.m/s$. c) is correct.