Question

Which of the following potential energy curves possibly describe the elastic collision of two billiard balls?

Here r is the distance between centres of the balls:

• A.
• B.
• C.
• D.

Answer 1

Answer: (C)

Answer 2

The potential energy of a system of two masses varies inversely as the distance (r) between them.

$i..e.v(r) \propto \frac{1}{r}$

When the two billiard balls touch each other, potential energy becomes zero

i.e. at r = R =2R, (v (r) =0

Out of the given graphs, only curve (3) satisfies these conditions. Therefore, all other curves cannot possibly describe the elastic collision of two billiard balls.