Question

Circular disc of mass 2 kg and radius 1 m is rotating about an axis perpendicular to its plane and passing through its centre of mass with a rotational kinetic energy of 8 J. The angular momentum in (J-s) is

• A. 8
• B. 4
• C. 2
• D. 1

Answer 1

Answer: (B)

Rotational kinetic energy $=\frac{1}{2}I{\omega }^2=8J$ $\Rightarrow$ $\frac{1}{2}\times \frac{1}{2}m{r}^2{\omega }^2=8$ or $\frac{1}{4}\times 2\times {(1)}^2{\omega }^2=8$ or ${\omega }^2=16$ or $\omega =4rad/s$ Angular momentum, $L=I\omega$ $=\frac{1}{2}m{r}^2\omega$ $=\frac{1}{2}\times 2\times {(1)}^2\times 4$ $=4J-s$