I know this equation has something to do with conservation of momentum. But when I plug in for the initial velocity 0 it cancels out the left side of the equation. So that doesn't work so I'm lost.. what should I do to solve this problem.

An object at rest on a flat, horizontal surface explodes into 2 fragments, one 7 times as massive as the other. The heavier fragment slides 8.2m before stopping. How far does the lighter fragment slide? Assume that both have the same coefficient of friction.

Can someone give me a formula to work with. I have no idea.