$A$ cube of side $40 \ cm$ is floating with $\frac{1}{4}$th of its volume immersed in water. When a circular disc is placed on the cube, it floats with $\frac{2}{5}$th of its volume immersed in water. The mass of the disc is (in $kg$)

$A$ block of wood floats in water with $\frac{4}{5}$ of its volume submerged,but it just floats in another liquid. The density of the liquid is (in $kg/m^3$):

$A$ solid cube and a solid sphere,both made of the same material,are completely submerged in water but at different depths. The sphere and the cube have the same surface area. The buoyant force is

The ratio of masses of a cubical block of wood and a chunk of concrete is $\frac{3}{5}$ so that the combination just floats with its entire volume submerged under water. If the specific gravity of wood is $0.5$,then the specific gravity of concrete will be:

$Assertion :$ The buoyant force on a submerged rigid object can be considered to be acting at the centre of mass of the object.
$Reason :$ For a rigid body,a force field distributed uniformly through its volume can be considered to be acting at the centre of mass of the body.

$A$ small metal sphere of density $\varrho$ is dropped from height $h$ into a jar containing liquid of density $\sigma$ $(\sigma > \varrho)$. The maximum depth up to which the sphere sinks is (Neglect damping forces).