Chapter 7, Problem 7.5DQ

A physics teacher had a howling hall suspended from a very long rope attached to the high ceiling of a large lecture hall. To illustrate his faith in conservation of energy, he would hack up to one side of the stage, pull the hall far to one side until the taut rope brought it just to the end of his nose, and then release it. The massive hall would swing in a mighty are across the stage and then return to stop momentarily just in front of the nose of the stationary, unflinching teacher. However, one day after the demonstration he looked up just in time to see a student at the other side of the stage push the hall away from his nose as he tried to duplicate the demonstration. Tell the rest of the story, and explain the reason for the potentially tragic outcome.