Question

At one point in its fall, a ball has a KE of 5J and a PE of 10J. It continues to fall and at another point has
a PE of 3J. What is the ball’s KE at this point?

Answer 1

The law of conservation of energy says

$$\rm KE_i+PE_i=KE_f+PE_f$$

Hence,

$$5\:\rm J+10\:\rm J=KE_f+3\:\rm J$$

$$\rm KE_f=12\:\rm J$$