I'm stuck on this problem. A sledge of mass 120 kg is at rest on a horizontal icy surface. A man of mass 70 kg stands at one end of the sledge so the initially the distance from the man to the shore is 20 m. The man now walks 3 m relative to the sledge, towards the shore. The he stops. Assuming the moves w/out friction, how far from the shore is the man when he stops. THis is pretty much all i know: 70(Rm)+120(Rs)=0 where Rm and Rs are the distances from the man to the cm and the cm of the sledge to the cm respectfully.