In which layer of the atmosphere is water vapour present?

The term 'fluid' is used for ............

$A$ closed rectangular tank is completely filled with water and is accelerated horizontally with an acceleration $a$ towards the right. Pressure is $(i)$ maximum at,and $(ii)$ minimum at:

$A$ hollow sphere of radius $R$ is filled completely with an ideal liquid of density $\rho$. The sphere is moving horizontally with an acceleration $2g,$ where $g$ is the acceleration due to gravity. If the minimum pressure of the liquid is $P_0$,then what is the pressure at the centre of the sphere?

$A$ $U$-tube contains water and methylated spirit separated by mercury. The mercury columns in the two arms are initially in level with $10.0 \; cm$ of water in one arm and $12.5 \; cm$ of spirit in the other. If $15.0 \; cm$ of water and spirit each are further poured into the respective arms of the tube,what is the difference in the levels (in $cm$) of mercury in the two arms? (The specific gravity of spirit is $0.8$.)

Why is the dam of a water reservoir thick at the bottom?