16 3 pts For thin-walled closed sections (of constant thickness), such as the one shown below, we can approximate the torsional constant J* as J* = 4tA/Lm, where A is the area enclosed within the median line and Lm is the path length. Compute the following. (a) Torsional stiffness (b) Rotation, (x1), if the length L of the body is 5 m (c) The shear stress in the thickest part of each body, using T = M/(2tAm) Use G = 25 GPa, M = -2.0e5 Nm (loaded in pure torsion), h = 0.7 m, b = 1.1 m, and t = 0.02 m. t t b h