Disc A of radius R is lying flat on a horizontal surface. Disc B is also at rest. Disc C, which is identical to B is traveling along the surface with its velocity parallel to the line joining the centre `C_(1) and C_(2)` of the discs A and B. The distance between the line `C_(1)C_(2)` and the line of motion of centre of disc C is `sqrt(3)r` , where `r` is radius of both B and C. Impact of C with B is completely elastic. Subsequently it is observed that both B and C just miss hitting the disc A. Find the radius (R) of A in terms of r.

Answer

`R=((sqrt(3)+1)/(sqrt(3)-1))r`