A air bubble of radius $1\,cm$ in water has an upward acceleration $9.8\, cm\, s ^{-2}$. The density of water is $1\, gm\, cm ^{-3}$ and water offers negligible drag force on the bubble. The mass of the bubble is$.......gm$

$\left( g =980 \,cm / s ^{2}\right)$

A hollow spherical shell at outer radius $R$ floats just submerged under the water surface. The inner radius of the shell is $r$. If the specific gravity of the shell material is $\frac{27}{8}$ $w.r.t.$ water, the value of $r$ is$......R$

The area of cross-section of the wider tube shown in figure is $800$ $cm^2$. If a mass of $12$ $ kg $ is placed on the massless piston, the difference in heights $h$ in the level of water in the two tubes is  ........ $cm$

A wooden block, with a coin placed on its top, floats in water as shown in fig. the distance $l $ and $h$ are shown there. After some time the coin falls into the water. Then

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

Acontainer of large surface area is filled with liquid of density $\rho$ .Acubical block of side edge $a$ and mass $M$ is floating in it with four-fifth of its volume submerged. If a coin of mass $m$ is placed gently on the top surface of the block is just submerged. $M$ is