A velocity distribution in a $2$ in $.$ diameter pipe is measured to be $u(r)=30(1-\frac{r^2}{r_o^2})\frac{ft}{sec},$ where

$r_o$ is the radius of the pipe and $r$ is the distance from the center of the pipe to the walls. Calculate

the shear stress at the wall for water? The kinematic viscosity of water is $1\mathrm{.}06{10}^{-5}\frac{f{t}^2}{sec}.$