16.35  (Fixed Axis Rotation)

The weight and radius of the friction disk A are W_A = 10 lb and r_A = 4.5 inch;  the weight and radius of the friction disk B are W_B = 4 lb and r_B = 3 inch.  The disks are at rest when a 5 lb-in couple moment M is applied to disk A.  Assume no slipping between the disks.
Determine:  (a)  The angular acceleration of each disk;  (b)  The friction force that disk A exerts on disk B.

Comments/Hints:
1.  Draw a separate free body diagram and kinetic diagram of each disk.  The FBD of disk A will have pin reactions, the couple M, the contact friction force (from disk B), and (if you wish) a contact normal force.  The KD of disk A will have an I_A·a_A term.  The FBD of disk B will have pin reactions, the contact friction force (from disk A, equal and opposite in direction), and (if you wish) a contact normal force.  The KD of disk B will have an I_B·a_B term.
2.  I_A = 0.02184 slug-ft², and I_B = 0.003882 slug-ft².
3.  Write moment equations, one for disk A and another for disk B.
4.  You need to relate a_A vs. a_B using kinematics:  You get a_B = 1.5a_A.
5.  Solve the two moment equations plus the kinematics equation to get:  a_A = 13.63 rad/s²;  a_B = 20.45 rad/s² ;  and F = 0.3175 lb.