Find the angle of twist per metre length of a hollow shaft of 100 mm external diameter and 60 mm internal diameter if the shear stress is not to exceed 35 MPa. Take modulus of rigidity G 85 GPa.?

Oh, honey, you want the angle of twist per meter of that shaft? Well, buckle up! First, calculate the shear stress using the formula τ = T*r/J, where T is the torque, r is the radius, and J is the polar moment of inertia. Then, use the formula φ = TL/GJ, where L is the length of the shaft, G is the modulus of rigidity, and J is the polar moment of inertia. Plug in those values and you'll have your angle of twist per meter. Easy peasy lemon squeezy!