Variation of atmospheric pressure with height from the Earth is ................

$A$ 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 $cm$.

$A$ $U$-shaped tube is partially filled with an incompressible liquid of density $1.2 \ g \ cm^{-3}$. Oil, which does not mix with the liquid, is poured into the left side of the $U$-tube until the liquid rises by $15 \ cm$ on the right side. If the density of the oil is $0.9 \ g \ cm^{-3}$, the oil level will stand higher than the liquid level on the right side of the $U$-tube by: (in $cm$)

Why is mercury used in a barometer?

Water stands up to height $h$ behind a dam as shown in the figure. The front view of the dam gate is also shown in the adjoining figure. The density of water is $\rho$ and the acceleration due to gravity is $g$. If the atmospheric pressure force is also considered,the point of application of the total force acting on the dam due to water above $O$ is:

Explain why you cannot make a decent cup of tea on a mountain.