Question

State if each of the following statements is true or false. Give reasons for your answer.
(a) In an elastic collision of two bodies, the momentum and energy of each body is ocnserved.
(b) Total energy of a system is always conserved, no matter what internal and external forces on the body are present.
(c) Work done in the motion of a body over a closed loop is zero for every force in nature.
(d) In an inelastic collision, the final kinetic energy is always less than the initial kinetic energy of the system.

Answer 1

(a) False. The total momentum and total energy of the system are conserved and not of each body.
(b) False. The external forces on the body may change the total energy of the body.
(c) False. Work done in the motion of a body over a closed loop is zero only when the body is moving under the action of conservative forces (like gravitational or electrostatic forces ). It is not zero when the forces are non-conservative e.g. frictional forces etc.
(d) True, because in an inelastic collision, some kinetic energy usually changes into tsome other form of energy.