Finding Velocity given the initial velocity and weight

[dtmirand]

Homework Statement

An 80-kilogram man jumps off a raft that weighs 100 kg. His initial velocity from jumping is 7 meters per second. Assuming that the friction resistance of the water is zero, the velocity of the raft after the man jumps will be?

Homework Equations

Vf^2= Vi^2 + 2aD

The Attempt at a Solution

I am trying to figure out the velocity of that raft after the man jumps, the question is confusing me on which variable I need to solve the problem. Any help?

 

[Nathanael]

Do you know about conservation of momentum?