Why do bubbles rise in a soda water bottle?

$A$ ball whose density is $0.4 \times 10^3 \ kg/m^3$ falls into water from a height of $9 \ cm$. To what depth does the ball sink in $cm$?

$A$ tub is filled with water and a wooden cube $10 \ \text{cm} \times 10 \ \text{cm} \times 10 \ \text{cm}$ is placed in the water. The wooden cube is found to float on the water with a part of it submerged in water. When a metal coin is placed on the wooden cube, the submerged part is increased by $3.87 \ \text{cm}$. The mass of the metal coin is . . . . . . gram. (Take water density as $1 \ \text{g/cm}^3$ and density of wood as $0.4 \ \text{g/cm}^3$)

$A$ wooden cube floats in water when a $200\,g$ mass is placed on it. When the mass is removed,the cube rises by $2\,cm$ above the water level. The side of the cube is ......... $cm$.

$A$ cylindrical block of wood of base area $30 \, cm^2$ floats in a liquid of density $900 \, kg/m^3$. The block is depressed lightly and then released. The time period of the resulting oscillations of the block is equal to that of a spring with a block of the same mass. The spring constant is equal to ........ $N/m$.

$A$ piece of steel has a weight $W$ in air,$W_1$ when completely immersed in water,and $W_2$ when completely immersed in an unknown liquid. The relative density (specific gravity) of the liquid is: