Question
Show that when a body is dropped from a certain height, the sum of its kinetic energy and potential energy at any instant during its fall is constant.
Solution
Conservation of energy during the free fall of a body.
Let a body of mass m lying at position A be moved to a position B through a height h as shown in the fig. below.
Fig. The free fall of the body is hown below.
The work done on the body is mgh.
The body is at rest at position B.
Therefore,
