COLLISIONS......

Question

A small bob of a pendulum relief from 30 degree to the vertical hits another bob of same mass and size lying at rest on the table vertically below the point of suspension after elastic collision the angular amplitude of the pendulum is

A.30º B.60º C.15º D.0º

Answer 1

Answer: D.0º

Let v be the velocity of A at time of collision, and final velocity of both of them be v₁ ​ and v₂ ​ since it is elastic collision, coeff. of restitution is 1. 

v=v_{2 ​} −v₁ ​ 

Conservation of momentum: 

mv=mv₁ ​ +mv₂ ​ 

Solving these two equations we get, v₂ ​ =v and v₁ ​ =0 

So, the pendulum A will come to rest and have angular amplitude to be zero.