Consider a Newtonian fluid $($specific gravity $SG=0\mathrm{.}9,$ kinematic viscosity

$u=4**{10}^{-4})$ squeeze by the moving plate at the top and fixed plate at the bottom. The former contains the maximum velocity $U_{\text{m}\text{a}\text{x}}=U_0$ amount the velocity profile $U(y)$ alone the $y-$axis, while the latter denoted as no$-$slip condition holds the minimum velocity $U_{\text{m}\text{i}\text{n}}=0.$ Given the velocity profile as follows, express both the magnitude and direction of shear stress ${}_{\text{m}\text{o}\text{v}\text{i}\text{n}\text{g}\text{p}\text{l}\text{a}\text{t}\text{e}}$ is the distance between two plates.

$\frac{U(y)}{U_0}=\frac{3}{2}\frac{y}{b}-\frac{1}{2}(\frac{y}{b}{)}^3,$