Select the correct alternative.

Options

A. Work done by kinetic friction on a body always results in a loss of its kinetic energy.
B. Work done on a body, in the motion of that body over a close loop is zero for every force in nature.
C. Total mechanical energy of a system is always conserved no matter what type of internal and external forces on the body are present.
D. When total work done by a conservetive force on the system is positive then the potential energy associated with this force decreses.

Answer

D

Explanation

Work done by kinetic friction on a body may increase its kinetic energy.
As for (b), it is true for consevative forces.
For (c ), internal forces must be conservative and work of external forces on the system must be zero.