One person drops a ball from the top of a building while ano

One person drops a ball from the top of a building while another person at the bottom observes its motion. Will these two people agree on the value of the gravitational potential energy of the ball-Earth system? On the change in potential energy? On the kinetic energy?

Solution

Potential energy, its change, kinetic energy all are scalar quantities. These are independent of coordinate system in which they are measured. For the potential energy an arbitrary reference line or point exists, so if for both observers the reference point or line is same then they will agree in absolute value of potential energy. The difference is potential energy and kinetic energy have define frame independent scalar values. So they will agree.