## Physics (10th Edition)

There is no external force, so the momentum is conserved. Therefore, the total momentum before the collision and after the collision has to be the same: $$p_{01}+p_{02}=p_{f1}+p_{f2}$$ So a) and c) are eliminated. Because the collision is elastic, kinetic energies are conserved, too. $$\sum KE_0=\sum KE_f$$ Therefore, d) is correct.