The thin circular ring of cross-sectional radius r, shown in Fig. P6.21, is subjected to...

The thin circular ring of cross-sectional radius r, shown in Fig. P6.21, is subjected to a distributed torque per unit length, . Determine the angle of twist at sections A and B in terms of T, a, and r. Assume that the radius a is large enough to permit the effect of curvature on the torsion formula to be neglected.