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### Work, Energy and Power NCERT Solutions Class 11 Physics - Solved Exercise Question 6.7

Question 6.7:
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 conserved.
(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
Solution:
(a) False
In an elastic collision, the total energy and momentum of both the bodies, and not of each individual body, is conserved.

(b) False
Although internal forces are balanced, they cause no work to be done on a body. It is the external forces that have the ability to do work. Hence, external forces are able to change the energy of a system.

(c) False
The work done in the motion of a body over a closed loop is zero for a conservation force only.

(d) True
In an inelastic collision, the final kinetic energy is always less than the initial kinetic energy of the system. This is because in such collisions, there is always a loss of energy in the form of heat, sound, etc.