At what speed will the velocity head of a stream of water be equal to $40 \ cm$ of $Hg$ (in $cm/sec$)?

Different heads are in Column - $I$ and their formulas are given in Column - $II$. Match them appropriately.

Column - $I$	Column - $II$
$(a)$ Velocity head	$(i)$ $\frac{P}{\rho g}$
$(b)$ Pressure head	$(ii)$ $h$
$(c)$ Potential head	$(iii)$ $\frac{v^2}{2g}$

$A$ manometer connected to a closed tap reads $4.5 \times 10^5 \text{ Pa}$. When the tap is opened,the reading of the manometer falls to $4 \times 10^5 \text{ Pa}$. The velocity of the flow of water is ........ $m/s$.

The reading of a pressure meter attached to a closed pipe is $4.5 \times 10^4 \ N/m^2$. On opening the valve,water starts flowing and the reading of the pressure meter falls to $2.0 \times 10^4 \ N/m^2$. The velocity of water is found to be $\sqrt{V} \ m/s$. The value of $V$ is . . . . . .

$A$ tank of height $15 \ m$ and cross-section area $10 \ m^2$ is filled with water. There is a small hole of cross-section area $a$ which is much smaller than the container,located at a height of $12 \ m$ from the base of the container. How much force should be applied with a piston at the top level,so that the water coming out of the hole hits the ground at a distance of $16 \ m$ (in $kN$)? (Take,density of water $\rho = 1000 \ kg \ m^{-3}$ and $g = 10 \ m/s^2$)

What is the Magnus effect?