The weight and radius of friction disk A are WA = 12 lb and rA = 6 in.; the weight and rad...

The weight and radius of friction disk A are WA = 12 lb and rA = 6 in.; the weight and radius of friction disk B arc WB = 6 lb and rB = 4 in. The disks are at rest when a couple M of moment 7.5 lb · in. is applied to disk A. Assuming that no slipping occurs between the disks, determine (a) the angular acceleration of each disk, (b) the friction force that disk A exerts on disk B.