Question

The angular momentum of a system as particle is conserved

• A. when no external force acts upon the system
• B. when no external torque acts upon the system
• C. when no external impulse acts upon the system
• D. when axis of rotation remains same

Answer 1

The correct option is B when no external torque acts upon the system

$\frac{d\overrightarrow{L}}{dt}=\overrightarrow{{\tau }_{ext}}$
When $\overrightarrow{{\tau }_{ext}}=0$, $\frac{d\overrightarrow{L}}{dt}=0$ $\Rightarrow \overrightarrow{L}=constant$ i.e $\overrightarrow{L}$ is conserved.