Question

The rotational kinetic energies of two fly wheels are equal. If the ratio of their moments of inertia is $1:4$, the ratio of their respective angular momenta is :

• A. $4:1$
• B. $2:1$
• C. $1:4$
• D. $1:2$

Answer 1

The correct option is D $1:2$

$I_1{\omega }_1^2=I_2{\omega }_2^2$

$I\omega =L$

$KE=\frac{L^2}{2I}$

$\frac{I_1}{I_2}=\frac{1}{4}$

then, $\frac{L_1^2}{I_1}=\frac{L_2^2}{I_2}$

$\frac{L_1}{L_2}=\frac{1}{2}.$