Which of the following potential energy curves in figure cannot describe the elastic collision of two billiard balls ? Here r is the distance between centres of the balls .

Explanation

Distance between centre of balls is 2R when both ball collide .
During every elastic collision , the shape of ball slightly changes .
In elastic collision potential energy converted into kinetic energy .
The potential energy of a system of two masses is inversely proportional to the separation between them .
` :. V prop 1/r`
Out of the given graph , curve (v) only satisfies these two consitions .Therefore , all other curves cannot possibly describe the elastic collision of two billiard balls .