What is the pressure on a swimmer $20 \, m$ below the surface of water in $atm$?

$A$ barometer tube reads $75 \,cm$ of $Hg$. If the tube is gradually inclined at an angle of $30^{\circ}$ with the horizontal,keeping the open end in the mercury container,then find the length of the mercury column in the barometer tube in $cm$.

The pressure at the bottom of a water tank is $4 P$,where $P$ is atmospheric pressure. If water is drawn out until the water level decreases by $\frac{3}{5}$ of its initial height,then the pressure at the bottom of the tank is .........

$A$ tank of oil has a height of $4 \,m$ and a density of $850 \,kg \,m^{-3}$. The gauge pressure at the bottom of the tank is (Given: $1 \,atm = 10^5 \,Pa$,Acceleration due to gravity $g = 10 \,m \,s^{-2}$) (in $\,kPa$)

$A$ manometer reads the pressure of a gas in an enclosure as shown in Figure $(a)$. When a pump removes some of the gas,the manometer reads as in Figure $(b)$. The liquid used in the manometers is mercury and the atmospheric pressure is $76 \; cm$ of mercury.
$(a)$ Give the absolute and gauge pressure of the gas in the enclosure for cases $(a)$ and $(b)$,in units of $cm$ of mercury.
$(b)$ How would the levels change in case $(b)$ if $13.6 \; cm$ of water (immiscible with mercury) are poured into the right limb of the manometer? (Ignore the small change in the volume of the gas).

$A$ tank is filled with a liquid of density $\rho$ up to a height $H$. The average pressure on the walls of the container is: