A 2.00 kg ball is attached to a ceiling by a 1.40 m long string. The height of the room is 3 m. What is the gravitational potential energy of the ball relative to the ceiling?
What is the gravitational potential energy of the ball relative to the floor?
(c) What is the gravitational potential energy of the ball relative to a point at the same elevation as the ball?
1 answer

For each of your questions, the gravitational P.E. is M g times the distance of the ball above the reference plane. "g" is the acceleration of gravity.
That distance is zero for part (c).
Now you calculate the others. One answer will be negative, if done correctly.
The answers should be in Joules.