Batman (mass = 90 kg) jumps straight down from a bridge into a boat (mass = 530 kg) in which a criminal is fleeing. The velocity of the boat is initially +20 m/s. What is the velocity of the boat after Batman lands in it?

Answer 1

The total momentum for motion along the water does not change, assuming the water applies negligible retarding friction along that direction as the boat stabilizes. Therefore
M * 20 = (M + m)V
V = M*20/(M+m)
= (530/620)*20 m/s = ?