Problem 7.4. Torsion of a hollow bar A circular bar of radius R = 200 mm is replaced by a hollow bar of inner and outer radii R, and Ro, respectively, with Ro/R = 2. If the two bars are made of the same material and can carry the same maximum torque, determine (1) the outer radius of the hollow bar, R., and (2) the mass ratio for the hollow and solid bars. , (0) D(L) ,(2L) R Ro R L M L Fig. 7.9. Circular bar with hollow segment.