Question

The flywheel of a machine having weight of 4500 N and radius of gyration of 2 m has cyclic fluctuation of speed from 125 r.p.m to 120 r.p.m. Assuming g = 10m/s^2, the maximum fluctuation of energy is

(a) 12822 N-m

(b) 24200 N-m

(c) 14822 N-m

(d) 12100 N-m

The question was posed to me in examination.

My doubt stems from Flywheel topic in chapter Turning Moment Diagrams and Flywheel of Machine Dynamics

Answer 1

Correct choice is (d) 12100 N-m

Easy explanation: Mass of flywheel = weight of flywheel/Acceleration due to gravity = 4500/10kg

 Moment of Inertia = mk^2

                   = 1800 kgm^2

ω1 = 2π/60 x 125rad/sec

ω2 = 2π/60 x 120rad/sec

Emax = 1/2 I(?)^2

                = 12087.2 N-m

                = 12100 Nm