(a) What is the gravitational potential energy U of the sloth Earth system if we take the reference point y = 0 to be (I) at the ground.

SOLUTION: The Key Idea here is that once we have chosen the reference point for y = 0, we can calculate the gravitational potential energy U of the system relative to that reference point.

The sloth drops to the ground. For each choice of reference point, what is the change in the potential energy of the sloth- Earth system due to the fall?

SOLUTION: The Key Idea here is that the change in potential energy does not depend on the choice of the reference point for y = 0; instead.