$A$ vertical triangular plate $ABC$ is placed inside water with side $BC$ parallel to the water surface as shown. The force on one surface of the plate by water is (density of water is $\rho$ and atmospheric pressure is $P_0$).

Two vessels $A$ and $B$ have the same base area and contain water to the same height,but the mass of water in $A$ is four times that in $B$. The ratio of the liquid thrust at the base of $A$ to that at the base of $B$ is (in $:1$)

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

The limbs of a $U$-tube are lowered into vessels $A$ and $B$,where vessel $A$ contains water. Some air is pumped out through the top of the tube at $C$. The liquids in the left limb (in vessel $A$) and the right limb (in vessel $B$) rise to heights of $10\, cm$ and $12\, cm$ respectively above the free surfaces of the liquids in the vessels. The density of liquid $B$ is ........ $g/cm^3$.

Explain the specific density or relative density of a substance.

Define relative density of a substance.