The $x$ component of velocity in a steady incompressible flow field in the $x y$ plane is $u=A e^{x / b} \cos (y / b),$ where $A=10 \mathrm{m} / \mathrm{s}, b=5 \mathrm{m},$ and $x$ and $y$ are measured in meters. Find the simplest $y$ component of velocity for this flow field.