Question

The time rate of the total angular momentum of a system of particles about a point (taken as the origin of our frame of reference) is equal to the sum of the external torques (i.e. the torques due to external forces) acting on the system taken about the same point. If τext = dL/dt Hence, if τext = 0, dL/dt = 0 Thus, if the total external torque on a system of particles is zero, then the total angular momentum of the system is conserved, i.e. it remains constant.

A circular ring having a diameter of 40cm and mass of 1 kg is rotating about an axis normal to its plane and passing through the center with a frequency of 10 rotations per second. Now, calculate the angular momentum about the axis of rotation.