Two uniform disks A and $B,$ eachwith a mass of $2kg,$ are connected by a $2\mathrm{.}5kg$ rod $CD$ as shown. A counterclockwise couple $M$ of moment $2\mathrm{.}25N-m$ is applied to disk A$.$ Knowing that the disks roll without sliding, determine $($a$)$the acceleration of the center of each disk, $($b$)$ the horizontal component of the force exerted on disk $B$ by pin $D.$