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. Find its angular momentum about the axis of rotation.

• A. $160\times {10}^{-5}$ rad/s
• B. $8.0\times {10}^{-5}$ rad/s
• C. $4.0\times {10}^{-5}$ rad/s
• D. $10\times {10}^{-5}$ rad/s

Answer 1

The correct option is A $160\times {10}^{-5}$ rad/s

The moment of inertia of the circular disc about its diameter is
$I=\frac{1}{4}M{r}^2=\frac{1}{4}\left(0.200kg\right)(0.04m{)}^2$
$=8.0\times {10}^{-5}kg-m^2.$
and the angular momentum about the axis of rotation is
$L=I\omega =(8.0\times {10}^{-5}kg-m^2)\left(20rad/s\right)$