All are cylindrical rods having radius of cross-section $R$ and mass of each rod $\dfrac{M}{4}$. Find the moment of inertia about $yy'$ axis:
$A$ and $B$ are identical point masses. $A$ is released as shown in the diagram at an angle $60^\circ$ from the vertical. Find $R$ if $B$ is able to reach point $C$ after elastic impact.