Question

The rotational kinetic energy of a body is $80J$ . If the moment of inertia of the body about the axis of rotation is $4\times {10}^{-7}kg{m}^2$, the angular momentum of the body is:

• A. $4\sqrt{2}\times {10}^{-3}Js$
• B. $8\sqrt{2}\times {10}^{-3}Js$
• C. $8\times {10}^{-3}Js$
• D. $4\times {10}^{-3}Js$

Answer 1

Answer: (C)

$8\times {10}^{-3}Js$

$K{E}_{rotational}=80J.$
$L=I\omega$

$I=4\times {10}^{-7}kg{m}^2$

$KE=\frac{I}{2}{\omega }^2=\frac{I^2{\omega }^2}{2I}$

$80=\frac{L^2}{2\times 4\times {10}^{-7}}$

$L=8\times {10}^{-3}Js$