$($Viscous flow$)$ In a certain viscous $($viscosity $),$ incompressible flow field with zero body forces the velocity components are

$u=ay-b(cy-y^2)$

$v=w=0$

where $a,b,$ and care constant.

$($a$)$ Use the Navier$-$Stokes equations to determine an expression for the pressuregradient in the $x$ direction.

$($b$)$ For what dependance of constant a on constants $b$ and $c($if any$)$ will the shearing stress. Tyy be zero at $y=0$ where the velocity iszero?

$($a$)\frac{\text{d}\text{e}\text{l}\text{p}}{\text{d}\text{e}\text{l}\text{x}}=$

$($b$)a=$