The assembly consisting of a uniform slender bar (mass m/5) and a rigidly attached unifo...

The assembly consisting of a uniform slender bar (mass m/5) and a rigidly attached uniform disk (mass 4m/5) is freely pinned to point O on the collar that in turn slides on the fixed horizontal guide. The assembly is at rest when the collar is given a sudden acceleration a to the left as shown. Determine the initial angular acceleration of the assembly.