Which of the following potential energy curves in Fig. 6.18 cannot possibly describe the elastic collision of two billiard balls? Here r is the distance between centres of the balls.

Two identical ball bearings in contact with each other and resting on a frictionless table are hit head-on by another ball bearing of the same mass moving initially with a speed VL If the collision is elastic, which of the following figure is a possible result after collision?

Two spherical balls are charged with 1.2 and 4.8 coulomb of charges. The distance between their centre is 120 cm. Find out the point where the forces neutralise each other.