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 $10\frac{rad}{s}$. Find the angular momentum about the axis of rotation.

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

The moment of inertia of the circular disc about its diameter is

$l=\frac{1}{4}M{r}^2=\frac{1}{4}\left(0.200kg\right){\left(0.04m\right)}^2$
$=8.0\times {10}^{-5}kg-m^2$.

The angular momentum about the axis of rotation is

$L=l\omega =(8.0\times {10}^{-5}kg-m^2)\left(10\frac{rad}{s}\right)$
$=8.0\times {10}^{-4}kg-\frac{m2}{s}=8.0\times {10}^{-4}J-s$.