A fixed non conducting smooth track is in the shape of a quarter circle of radius R in vertical plane. A small metal ball A is fixed at the bottom of the track. Another identical ball B, which is free to move, is placed in contact with ball A. A charge Q is given to ball A which gets equally shared by the two balls. Ball B gets repelled and ultimately comes to rest in its equilibrium position where its radius vector makes an angle `theta (theta lt 90^(@))` with vertical. Mass of ball is m. Find charge Q that was given to the balls.

Answer

`Q=8Rsin((theta)/(2))sqrt(2piepsilon_(0)mgsin((theta)/(2)))`