An object at rest on a flat, horizontal surface explodes into two fragments, one five times as massive as the other one. The lighter fragment gains a velocity of 10 m/s in the left direction right after the explosion. On the other hand, the heavier fragment gains a velocity of v in the right direction after the explosion and slides 50 cm in the right direction before stopping. Find the kinetic frictional coefficient between the heavier fragment and the surface.