Work, Power and Energy

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Question : 8
Total: 30
Answer carefully, with reasons :
(a) In an elastic collision of two billiard balls, is the total kinetic energy conserved during the short time of collision of the balls (i.e. when they are in contact)?
(b) Is the total linear momentum conservedduring the short time of an elastic collision of two balls?
(c) What are the answer to (a) and (b) for an inelastic collision?
(d) If the potential energy of two billiard balls depends only on the separation distance between their centres, is the collision elastic or inelastic?
(Note, we are talking here of potential energy corresponding to the force during collision, not gravitational potential energy).
Solution:  
(a) During collision (when balls are in contact), the kinetic energy of balls gets converted into potential energy. Kinetic energy before collision and after collision is the same. Thus during the given elastic collision, the total kinetic energy is not conserved.
(b) Yes, the total linear momentum is conserved during the short time of an elastic collision of two balls.
(c) The total kinetic energy is not conserved in an elastic collision, during collision and after collision. The total momentum of the two balls is conserved.
(d) It is elastic collision.
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