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) In this case total kinetic energy is not conserved when hte bodies are in contact dining elastic collision even, the kinetic energy is converted into potential energy.
Yes, because total momentum conserves as per law of conservation of momentum.
c) the answer remain unchanged.
d) it is a case of elastic collision because in this case the forces will be of conservative nature.