The velocity profile between two disks with the top disk rotating is given as v = r z H , where is the rotational speed of the rotating disk, H is the height between the two disks, and r is the radial distance from the center of the disk. Show that:

(a) (4 points) The shear stress is given as *r**H .

b) (6 points) The torque of the disk is given as (***R^4) / (2H) , where R is the radius of the disk.