Here is another one of these spool problems: A large spool of rope stands on the ground with the end of the rope lying on the top edge of the spool. A person grabs the end of the rope and walks a distance L, holding onto it. The spool rolls behind the person without slipping. (a) What length of rope unwinds from the spool? (b) How far does the spool's center of mass move? I really haven't a clue on what to do here. I know there is a torque causing the spool to move, but that doesn't help me much. All I can say for sure is that the answer to (a) must be less than L. Any tips?