P6.031 A conveyor belt is driven by a 9-hp motor turning at 1,200 rpm. Through a series of gears that reduce the speed, the motor drives the belt drum shaft at a speed of 14 rpm. If the allowable shear stress is 8.8 ksi and both shafts are solid, calculate (a) the required diameter of the motor shaft. (b) the required diameter of the belt drum shaft. Answers: (a) motor shaft d = lin. (b) belt drum shaft d = Jin.