The 5-kg cylinder is initially at rest when it is placed in contact with the wall $B$ and the rotor at $A .$ If the rotor always maintains a constant clockwise angular velocity $\omega=6 \mathrm{rad} / \mathrm{s},$ determine the initial angular acceleration of the cylinder. The coefficient of kinetic friction at the contacting surfaces $B$ and $C$ is $\mu_{k}=0.2$.