Question

A uniform circular disc of mass 200 g and radius 4.0 cm is rotated about one of its diameter at an angular speed of 20 rad/s. Its angular momentum about the axis of rotation is (in kg-$m^2$/s)

• A. $16.0\times {10}^{-4}$
• B. $8.0\times {10}^{-4}$
• C. $4.0\times {10}^{-4}$
• D. $10\times {10}^{-4}$

Answer 1

The correct option is A

$16.0\times {10}^{-4}$

The moment of inertia of the circular disc about its diameter is $\text{I}=\frac{1}{4}M{r}^2=\frac{1}{4}$ $\left(0.2\right)$ $(1.14{)}^2$ $=8.0\times {10}^{-5}$ kg - $m^2$ and the angular momentum about the axis of rotation is $L=I\omega =(8.0\times {10}^{-5})\left(20\right)$