A body falls towards earth in air. Will its total mechanical energy be conserved during the fall? Justify.
The mechanical energy of a body is not conserved when the body is under a free-fall condition under the force of gravity. The force of air molecules acts against the motion of the body as in case of free fall, and hence the mechanical energy is not conserved. However, in the case of vacuum as a medium, the free-falling body has no force acting against the motion, and hence the energy is conserved.