고체역학 (Beer) — Torsion: Problem 3.91

3.91 In the stepped shaft shown, which has a full quarter-circular fillet, $D = 1.25\text{ in.}$ and $d = 1\text{ in.}$ Knowing that the speed of the shaft is $2400\text{ rpm}$ and that the allowable shearing stress is $7500\text{ psi}$, determine the maximum power that can be transmitted by the shaft.