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

No , kinetic energy is not conserved during the short time of collision . In in elastic collision , the kinetic energy before collision is equal to the kinetic energy after collision .
However , some of kinetic energy is converted into potential energy during the short time of collision of the balls .
(b) Yes , linear momentum remains conserved during the short time of an collision of two balls .
(c ) Linear momentum is conserved during an inelastic collision because there is no external force on the system of two balls . But the kinetic energy is not conserved during the collision or even after the collision .
(d) The collision is elastic . Since potential energy depends upon distance only , and the forces involved are conservative in nature .