Two disks are mounted on frictionless bearings on the same axle and can be brought together so that they couple and rotate as one unit. The first disk, with rotational inertia 1.4 kg·m2 is set spining at 420.0 rpm. The second disk, with rotational inertia 7.7 kg·m2, is set spinning at 615 rpm. Then they are coupled together in an inelastic collision.
a) What is their angular speed in radians per second after coupling?
b) If instead the second disk is set spinning at 615 rpm in the direction opposite the first disk's rotation, what is the angular speed after coupling?