Example: A container whose height is $200$ metres is filled with water and

a hole is placed at a height h from the surface of the liquid. The velocity of

the water leaving the hole is $40$ m$/$s$.$ Find the value of h if the acceleration

due to gravity is taken as $10$ m$/$s$^2.$If the flow constriction in a pipe, as shown in Fig. $4\mathrm{.}12,$ is well streamlined, the loss of

energy is practically equal to zero. The difference in velocity heads, $(\frac{V^2}{2}(g)),$ at two sections

across the constriction results in a change in potential heads, $h_{pz}=(\frac{p}{})+z.$ Such a device is

used for metering the quantity of flow $Q$ in the pipe system by measuring the difference in

potential head.