The velocity distribution in a $3-cm$ diameter pipe is given by

$u(r)=u_{\text{m}\text{a}\text{x}}[1-(\frac{r}{r_0}{)}^2]$

where $r_0$ is the pipe radius. Calculate the shear stress $($a$)$ at the centerline, $($b$)$ at $r=0\mathrm{.}25cm,$ and $($c$)$ at the wall, if water at $20C$ is flowing and $u_{\text{m}\text{a}\text{x}}=30\frac{m}{s}.$

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