Solution
= Solution
The steady rectilinear equation is $u''(y)=-G$, with no-slip conditions $u(0)=0$ and $u(a)=U$. Two integrations give the <Couette-Poiseuille flow>
$$
\boxed{\mathbf u(y)=\left[\frac{Uy}{a}+\frac G2y(a-y)\right]\widehat x,\qquad v=w=0.}
$$
The first term is driven by the moving wall and the second by the specified pressure gradient.