2(b) A solid steel shaft in a rolling mill transmits 20 kW of power at 2 Hz. Determine the smallest safe diameter of the shaft if the shear stress is not to exceed 40 MPa and the angle of twist is limited to 6° in a length of 3 m. Use G = 83 GPa. (Note that there are two conditions (Callow and (max) and they must be "used" separately). it