Consider the thin-walled tube of Fig. 5-26. Use the formula for shear stress, \(\tau_{\text {avg }}=T / 2 t A_{m}\), Eq. 5-18, and the general equation of shear strain energy, Eq. 14-11, to show that the angle of twist of the tube is given by Eq. 5-20. Hint: Equate the work done by the torque \(T\) to the strain energy in the tube, determined from integrating the strain energy for a differential element, Fig. 14-4, over the volume of material.