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 $p2,$ hence $($p$1-$p$2)$

Apply mass balance to relate $v2$ to $v1$

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

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