What is the angular momentum of a 2.4 kg uniform cylindrical grinding wheel of radius 12 cm when rotating at 1800 rpm?

Question

How much torque is required to stop it in 4.0 s?

Answer 1

Convert 1800 rpm to radians per second and call it w. (It texts, it's usually a Greek lower case omega)

The angular momentum is I w, where I is the moment of inertia. Use units of kg m^2/s

For a solid cylinder of mass M and radius R, I = (1/2) M R^2.

The torque L required to stop in time T is I w/T. The units will be newton meters or kg m^2/s^2 (same thing)