Asked by Hang
Your daredevil friends attach a rope to a 140kg sled that rests on a frictionless icy surface. The rope extends horizontaly to a smooth dead tree trunk lying at the edge of a cliff. Another person attaches a 30kg rock at the end of the rope after it passes over the tree trunk and then releases the rock--the rope is initially taut. A hanging rock of unknown mass accelerates downward at 2.7 m/s^2 and pulls the sled with it. Determine the mass of the hanging rock and the force that the rope exerts on the sled. There is no friction between the rope and the tree trunk.