As the diagram for the question is not given, lets answer the question generally.
Explanation:
Energy in a system is neither created nor destroyed. Yet, the energy can be changed from one form to another. If in the beginning, at a point a, an object has a potential energy of 100 joules, then at point b the kinetic energy of the object will be subtracted from the total 100 joules of energy present in the beginning. This is because the potential energy will be being changed to the kinetic energy and no new energy will be created or destroyed.
