State if each of the following statements is true or false

cbse
workandenergy

#1

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


#2

(i) False, in elastic collision the linear momentum and kinetic energy of the system as a whole is conserved, but momentum and kinetic energy of each of individual body change.
(ii) False, internal as well as external forces can change the kinetic energy. Again forces if conservative may change the potential energy of a system.
(iii) False, for non-conservative force the work done over a closed
loop is not zero.
(iv) It is usually true but not always true. As an example in the explosion of a cracker final kinetic energy is greater than the initial kinetic energy.
Again final kinetic energy of gun-bullet system after firing is more than initial kinetic energy before collision.