Define pressure. Give the $SI$ and $CGS$ unit of pressure.

$A$ $U$-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 $0.8$.)

Two liquids of densities $\rho_{1}$ and $\rho_{2}$ (where $\rho_{2} = 2\rho_{1}$) are filled behind a vertical wall of height $10 \; m$ and width $w$,as shown in the figure. Each liquid has a height of $h = 5 \; m$. The ratio of the force exerted by the upper liquid on the part $MN$ to the force exerted by the lower liquid on the part $NO$ is (Assume that the liquids do not mix):

An open $U$-tube contains mercury. When $11.2 \,cm$ of water is poured into one of the arms of the tube, how high does the mercury rise in the other arm from its initial level (in $\,cm$)?

$A$ bubble from the bottom of a lake rises to its surface. Its volume doubles in the process. Assuming isothermal conditions, atmospheric pressure $= 75 \, cm$ of $Hg$, and the ratio of the densities of mercury and water $= 40/3$. The depth of the lake will be ..... $m$.

In making an alloy,a substance of specific gravity $s_1$ and mass $m_1$ is mixed with another substance of specific gravity $s_2$ and mass $m_2$; then the specific gravity of the alloy is