Two identical balls each of radius $R$ collides head-on elastically. The following graphs represent

Question

Two identical balls each of radius $R$ collides head-on elastically. The following graphs represent the variation of potential energy $U(r)$ as a function of $r$, where $r$ is the distance between the centers of the balls. Identify the possible variation of $U$.

Professor PC Thomas Classes · Answer

Note that $r$ is the distance between the centers of the balls. Therefore, potential energy becomes zero only when $r=2 R$. As $r$ becomes lesser than $2 R$, the potential energy approaches infinity.