Consider fluid flow over a surface with a velocity profile given as u(y) = 100(y + 2y^2  0.5y^3) m/s. The dynamic viscosity for air and liquid water at 20C are 1.825  105 kg/ms and 1.002  103 kg/ms, respectively. Determine the shear stress at the wall surface, if the fluid is air at 1 atm and at a temperature of 20C.