8.10 There is a fully developed laminar flow of air between parallel plates. The upper plate moves at 5 ft/s and the spacing between the plates is a = 0.1 in.

(a) Assume that the air is incompressible and determine the flow rate per unit depth for the case of zero pressure gradient and the shear stress distribution across the channel.

(b) Determine the magnitude and direction of the pressure gradient that will give zero shear stress at y = 0.25a and determine the magnitude and direction of the shear stress at both surfaces.