Answer:
a) closely, a perfectly elastic collision.
Explanation:
A collision between two billiard balls is
a) closely, a perfectly elastic collision.
Since, the billiards table is quite smooth and resistance to ball movements are negligible. The Kinetic energy can be assumed to be conserved. And be it any collision momentum is always conserved. Hence, A collision between two billiard balls can be considered as closely, a perfectly elastic collision.
