The bob A of a pendulum released from horizontal to the vertical hits another bob B of the same mass at rest on a table as shown in figure.
If the length of the pendulum is 1m, calculate
(a) the height to which bob `A` will rise after collision.
(b) the speed with which bob `B` starts moving.
Neglect the size of the bobs and assume the collision to be elastic.

Options

A. `4.47 m s^(-1)`
B. `5.47 m s^(-1)`
C. `6.47 m s^(-1)`
D. `3.47 m s^(-1)`

Answer

A

Explanation

As the collision is elastic and two bobs have the same mass, therefore bob A transfers its entire momentum to the bob B and bob A does not rise at all. After collision, bob A comes to rest and ball B moves with speed of bob A
`therefore` The speed with which bob B starts moving is
` v=sqrt(2gh)=sqrt(2xx10 ms^(-2)xx1 m)=sqrt(20)ms^(-1)`
`=4.47 m s^(-1)`