a$)$ Consider a fully developed turbulent flow in between two parallel stationary plates with a gap of $2h$ between two plates. Use the overall force balance to show that the wall shear 'stress, ${}_w$; may be expressed as:

${}_w=\frac{hp}{L}$

Water is flowing through the above two horizontal plates duct which is $15m$ long with a gap between the two plates, $2h=30mm.$ If the total pressure drop, $p,$ over this length $($i$.$e$.15m)$ is $280*kPa,$ calculate the wall shear stress, ${}_w$ and the friction velocity, $u_r$