Question

A flywheel is rotating about a fixed axis passing through its COM. It has a kinetic energy of $420\text{Joules}$ when its angular speed is $20\text{rad/s}$. The moment of inertia of the wheel about the fixed axis is

• A. $1.44{\text{kg m}}^2$
• B. $2.1{\text{kg m}}^2$
• C. $1.9{\text{kg m}}^2$
• D. $0.48{\text{kg m}}^2$

Answer 1

The correct option is B $2.1{\text{kg m}}^2$

Given, angular speed $\left(\omega \right)=20\text{rad/s}$
Kinetic energy $(K.E)=420\text{J}$
As we know that, rotational kinetic energy of flywheel is
$K.E=\frac{1}{2}I{\omega }^2$
$\Rightarrow I=\frac{2K.E}{{\omega }^2}=\frac{2\times 420}{(20{)}^2}=2.1{\text{kgm}}^2$