$A$ boy has a mass of $60\, kg$. He wants to swim in a river with the help of a wooden log. If the relative density of the wood is $0.6$,what is the minimum volume of the wooden log required? (Density of river water is $1000\, kg/m^3$)

$A$ cube of external side length $10 \ cm$ has an inner cubical cavity of side length $5 \ cm$. The density of the inner portion is twice that of the outer portion. If this cube is just floating in a liquid of density $2 \ g/cm^3$, find the density of the inner portion.

$A$ cylindrical block of area of cross-section $A$ and of material of density $\rho$ is placed in a liquid of density one-third of the density of the block. The block compresses a spring,and the compression in the spring is one-third of the length of the block. If the acceleration due to gravity is $g$,the spring constant of the spring is:

$A$ cylinder of mass $m$ and material density $\rho$ hanging from a string is lowered into a vessel of cross-sectional area $A$ containing a liquid of density $\sigma$ $(< \rho)$ until it is fully immersed. The increase in pressure at the bottom of the vessel is

State the law of floatation.

$A$ wooden block of volume $1000\, cm^3$ is suspended from a spring balance. It weighs $12\, N$ in air. It is suspended in water such that half of the block is below the surface of water. The reading of the spring balance is ...... $N$.