For a certain engine having an average speed of 1200 rpm, a flywheel approximate as a solid disc, is required for keeping the fluctuation of speed within 2% about the average speed. The fluctuation of kinetic energy per cycle is found to be 2kJ. What is the least possible mass of the flywheel if its diameter is not to exceed 1m?
(a) 40 kg (b) 51 kg
(c) 62 kg (d) 73 kg