Question

For a certain engine having an average speed of 1200 rpm, a flywheel approximated 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 2 kJ. What is the least possible mass of the flywheel if its diameter is not to exceed 1 m ?

(a) 40 kg

(b) 51 kg

(c) 62 kg

(d) 73 kg

I had been asked this question by my school teacher while I was bunking the class.

My question comes from Flywheel in division Turning Moment Diagrams and Flywheel of Machine Dynamics

Answer 1

Right answer is (b) 51 kg

To explain: Given N = 1200 rpm, ΔE = 2kJ = 2000 J, D = 1m, Cs = 0.02

Mean angular speed of engine,

ω = 2πN/60 = 125.66 rad/ sec

Fluctuation of energy of the flywheel is given by,

ΔE = Iω^2Cs = 1/2mR^2ω^2Cs       For solid disc I = mR^2/2

m = 51 kg