Wow, thanks guys for the prompt responses.
Okay so I need to use the conservation of Energy theorem?
1/2*M*V^2?
Eh?
Solve For Mass, and Plug that Back into the Conservation of Momentum?
Homework Statement
A HOCKEYPLAYER SKATES AT 7.85 M/S AND HAS A MASS OF 120 KG WHEN HE COLLIDES WITH ANOTHER STAIONARY HOCKEY PLAYER. THE SECOND HOCKEY PLAYER IS NOW MOVING AT 5.67 M/S. FIND THE MASS OF THE SECOND HOCKEY PLAYER AND THE SPEED OF THE FIRST. ASSUME THIS COLLISION IS ELASTIC...