Question

A flywheel connected to a punching machine has to supply energy of 400 Nm while running at a mean angular speed of 20 rad/s. If the total fluctuation of speed is not to exceed $\pm$2% the mass moment of inertia of the flywheel in kg-$m^2$ is

• A. 25
• B. 50
• C. 100
• D. 125

Answer 1

The correct option is A 25

$\Delta E=400Nm,{\omega }_{mean}=20\text{rad/s}$

$C_s=\pm 2\%=4\%=\frac{4}{100}$

$\Delta E=I{\omega }_{mean}^2{C}_s$

$400=I\times {\left\{20\right\}}^2\times \left\{0.04\right\}$

$I=25kg{m}^2$