A thin cylinder is turning about its axis. Find the safe number of revolutions for a rotor of 3 metres in diameter if the hoop stress is not to exceed 1300 kg/cm. Take density as 6500 kg/cm. 3 A machine is driven by a motor, which delivers a constant torque. The resisting torque of the machine increases uniformly from 500 Nm to 1500 Nm through one revolution of the driving shaft and drops suddenly to 500 Nm again at the beginning of the next revolution. The mean speed of the machine shaft is 300 rpm. In order to maintain coefficient fluctuation of speed of the machine as 0.2, a solid circular steel disc of 25 mm thick is used as a flywheel. The mass density of steel is 7800 kg/m. Evaluate the diameter of the flywheel disc.