Adisk of mass m and radius r rotates at angular velocity ω0. another disk of mass m and radius r is dropped on top of the rotating disk such that their centers coincide. both disks now spin at a new angular velocity ω. what is ω?

Explanation:

As we know that there is no external torque on the system of two disc

then the angular momentum of the system will remains conserved

So we will have

now we have

also we have

now from above equation we have

now we have

grav forces affect all objects magnetic forces affect magnetic objects and electric currents

not too sure thinking all accelerations are pointed down