Batman (mass = 101 kg) jumps straight down from a bridge into a boat (mass = 500 kg) in which a criminal is fleeing.

The velocity of the boat is initially +14 m/s. What is the velocity of the boat after Batman lands in it?

in m/s

not sure about how many dimensions we are working with, and if there are two, then whats really going on, and why its different than one.

So in other words, what makes it two? thanks alot.