In a $U$-tube as shown in the figure,water and oil are in the left and right sides of the tube,respectively. The heights from the bottom for the water and oil columns are $15 \; cm$ and $20 \; cm$,respectively. The density of the oil is ...... $kg/m^3$. [Take $\rho_{\text{water}} = 1000 \; kg/m^3$]

$A$ liquid $X$ of density $3.36 \, g/cm^3$ is poured into a $U$-tube containing $Hg$ up to a height of $10 \, cm$. Another liquid $Y$ is poured into the left arm to a height of $8 \, cm$. The upper levels of $X$ and $Y$ are at the same height. Find the density of liquid $Y$ in $g/cm^3$. (Density of $Hg = 13.6 \times 10^3 \, kg/m^3$)

$A$ liquid mixture of volume $V$ has two liquids as its ingredients with densities $\alpha$ and $\beta$. If the density of the mixture is $\sigma$,then the mass of the first liquid in the mixture is ............

Define relative density of a substance.

The density changes with pressure for which fluid? Give reason.

$A$ force of $F = 10 \ N$ is exerted on a surface of area $A = 0.1 \ m^{2}$ at an angle of $60^{\circ}$ with the surface. Find the pressure produced on this surface.