Question

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 rad/s. Find the angular momentum about the axis of rotation

• A. $4\times {10}^{-4}J-s$
• B. $8\times {10}^{-4}J-s$
• C. $4\times {10}^{-8}J-s$
• D. $8\times {10}^{-8}J-s$

Answer 1

The correct option is B

$8\times {10}^{-4}J-s$

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

$I$ = $\frac{1}{4}M{r}^2$ = $\frac{1}{4}\left(0.200kg\right)(0.04m{)}^2$

= $8.0\times {10}^{-5}kg-m^2$

The angular momentum about the axis of rotation is

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

= $8.0\times {10}^{-4}kg-m^2/s$ = $8.0\times {10}^{-4}J-s$