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 ( in kg-m/s) about the axis of rotation.

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

Answer 1

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

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
$L=l\omega =(8.0\times {10}^{-5}kg-m^2)\left(20rad/s\right)$