A solid steel shaft, 90 mm in diameter is coupled in series to a hollow shaft with an external diameter of 100 mm and internal diameter of 90 mm. Calculate the torsional stiffness of 1 mm length of...

A solid steel shaft, 90 mm in diameter is coupled in series to a hollow shaft with
an external diameter of 100 mm and internal diameter of 90 mm. Calculate the
torsional stiffness of 1 mm length of each of these shafts if they are used
separately and compare this with the torsional stiffness of a 1 m length of the
compound shaft consisting of a 0.5 m length of each of the shafts mentioned
above. (G = 80 GPa)