Anwer 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)?
Is the total linear momentum conserved during the short time of an elastic collision of two balls?
c) What are the answers to a) and b) for an inelastic collision?
d) If the potenital energy of two billiard balls depends only on the separation distance between their centers, is the collision elastic or inelastic? (note we are talking here of potential energy corresponding to the force during collision, not gravitational potential energy).

Explanation

(a) No, K.E. is not conserved during the given elastic collision. K.E. before and after collision is the same. Infact, during collision, K.E. of the balls gets converted into potential energy.
(b) Yes, the total linear momentum is conserved during the short time of an elastic collision of two balls.
(c) In an inelastic collision, total K.E. is not conserved during collision and even affter collision.The total linear momentum is however, conserved during as well as after collision.
(d) The collision is elastic, because the forces involved are conservative.