(C) Prove that a hollow shaft is stronger and stiffer than a solid shaft of same length and weight and made of same material. (D) A solid cylindrical shaft is to transmit 300 kW at 100 r.p.m. (i) If the shear stress is not to exceed 80 MPa, find the diameter of the solid shaft. (ii) What percentage saving in weight would be obtained if the solid shaft is replaced by a hollow one whose internal diameter is equal to 0.6 times of the external diameter. Assume the length, the material and maximum shear stress will be the same for both the shafts.