Disk a, with a mass of 8.0 kg and a radius of 90 cm , rotates clockwise about a frictionless vertical axle at 50 rev/s . disk b, also 8.0 kg but with a radius of 10 cm , rotates counterclockwise about that same axle, but at a greater height than disk a, at 50 rev/s . disk b slides down the axle until it lands on top of disk a, after which they rotate together.