The angular momentum of a system of particles is conserved

Options

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

B

Explanation

We know that `tau_(ext)=(dL)/(dt)` if angular momentum is conserved, it means change in angular momentum = 0
or `dL=0" "(dL)/(dt)=0impliestau_(ext)=0`
Thus total external torque = 0