The diagram shows a simple mercury barometer. Which of the following does not cause the height of the mercury column to vary?

At what speed,the velocity head of water is equal to the pressure head of $40 \, cm$ of mercury? (Given: Density of mercury = $13.6 \times 10^3 \, kg/m^3$,Density of water = $10^3 \, kg/m^3$,$g = 9.8 \, m/s^2$)

The pressure acting on a submarine is $3 \times 10^{5} \; Pa$ at a certain depth. If the depth is doubled,the percentage increase in the pressure acting on the submarine would be: (Assume that atmospheric pressure is $1 \times 10^{5} \; Pa$,density of water is $10^{3} \; kg \; m^{-3}$,and $g = 10 \; m \; s^{-2}$)

$A$ barometer tube reads $76 \ cm$ of mercury. If the tube is gradually inclined at an angle of $60^\circ$ with the vertical,keeping the open end immersed in the mercury reservoir,the length of the mercury column will be ........ $cm$.

Show that the pressure produced due to a fluid column depends on the height of the fluid column and the density of the fluid.

During a blood transfusion,a needle is inserted into a vein where the gauge pressure is $2000\,Pa$. At what height must the blood container be placed so that blood may just enter the vein (in $,m$)? (Density of blood $= 1.06 \times 10^3\,kg/m^3$ and take $g = 9.8\,m/s^2$).