Question

Circular disc of mass $2kg$ and radius $1m$ is rotating about an axis perpendicular to its plane and passing through its centre of mass with a rotational kinetic energy of $8J$.

The angular momentum in ($Js$) is:

• A. $8$
• B. $4$
• C. $2$
• D. $1$

Answer 1

Answer: (B)

$4$

angular momentum and rotational kinetic energy are related as
$K.E=\frac{L^2}{2I}\Rightarrow 8=\frac{L^2}{2\times (2\times (1{)}^2)}$
$I=m{R}^2=2(1{)}^2=2$
$\Rightarrow L^2=16$ or $L=4J{s}^{-1}$