Water flows through the pipe contraction shown in the figure below. For the given $0\mathrm{.}2-m$ difference in manometer level, determine the flowrate as a function of the diameter of the small pipe, $D.$

Hint:

$,$ Apply hydrostatics to determine $p1$ and p$2,$ hence $($p$1-$p$2)$

Apply Bernoulli's equation between points $1$ and $2$ to determine $v1.$ Note that $z1=z2$ and $v2=0.$

$,$ Find the volumetric flowrate in $\frac{m^3}{s}$ using $Q=A1*{*}_{v1}$