Correct Answer : All of the above
Explanation : * If two equal and perfectly elastic smooth spheres impinge directly, they interchange their velocities.
* If a smooth sphere impinges on another sphere, which is at rest, the latter will move along the line of centres.
* If two equal spheres which are perfectly elastic impinge at right angles, their direction after impact will still be at right angles.
* If a sphere impinges directly on an equal sphere which is at rest, then a fraction (1 - e2) the original kinetic energy is lost by the impact.
