$A$ body floats in a liquid contained in a beaker. If the whole system as shown in the figure falls freely under gravity, then the upthrust on the body due to the liquid is

$A$ cube having a side of $10 \ cm$ with unknown mass $m$ and a $200 \ g$ mass were hung at two ends of a uniform rigid rod of $27 \ cm$ length. The rod along with the masses was placed on a wedge,keeping the distance between the wedge point and the $200 \ g$ weight as $25 \ cm$. Initially,the masses were not in balance. $A$ beaker is placed beneath the unknown mass and water is added slowly to it. At a given point,the masses were in balance and half the volume of the unknown mass was submerged in the water. (Take the density of the unknown mass to be greater than that of water,the mass did not absorb water,and the water density is $1 \ g/cm^3$). The unknown mass $m$ is . . . . . . $kg$.

$A$ streamlined body falls through air from a height $h$ on the surface of a liquid. If $d$ and $D$ $(D > d)$ represent the densities of the material of the body and the liquid respectively,then the time after which the body will be instantaneously at rest is:

$A$ wooden cylinder floats vertically in water with half of its length immersed. The density of wood is

Construction of submarines is based on

State the law of floatation and describe its cases.