Question

A uniform circular disc of mass $200g$ and radius $5cm$ is rotated about one of its diameters at an angular speed of $15rad/sec$ What is the angular momentum about the axis of rotation?

• A. $16Js$
• B. $18.75Js$
• C. $19Js$
• D. $22Js$

Answer 1

Answer: (B)

Moment of inertia of disc about the diameter
$I=\frac{M{R}^2}{4}$
$=\frac{1}{4}\times 200\times 10^{-3}\times {\left(5\times 10^{-2}\right)}^2$
$I=\frac{0.2\times 25\times 10^{-4}}{4}=\frac{5\times 10^{-4}}{4}$ (Given $\omega =15rad/s)$
$\therefore L=I\omega =\frac{5\times 10^{-4}}{4}\times 15=\frac{75}{4}\times 10^{-4}$
$=18.75\times 10^{-4}J-s$