Question

The bob A of a pendulum released from 30º to be vertical hits another bob B of the same mass at rest on a table as shown in fig. given below. How high does the bob A rise after the collision? Neglect the size of the bobs and assume the collision to be elastic.

Answer 1

We know that in perfectly elastic head on collision, when two equal masses collide with each other, then they exchange their speeds.

In the present case, bob A is moving with certain speed and bob B is at rest. Hence after collision, bob A comes to rest and the bob B starts moving with the speed of the bob A. The bob A transfers whole of its momentum to bob B and hence bob A, will not rise at all after the collision.