A $U$ tube contains water and methylated spirit separated by mercury . The mercury columns in the two arms are at the same level with $10\,cm$ of water in one arm and $12.5\,cm$ of spirit in the other as shown in figure. The relative density of the spirit is

An engine pumps water through a hose pipe. Water passes through the pipe and leaves it with a velocity of $2\, m/s$. The mass per unit length of water in the pipe is $100\, kg/m$. ......... $W$ is the power of the engine .

If work done in increasing the size of a soap film from $10\, cm\times6\, cm$ to $60\, cm\times11\, cm$ is $2\times10^{-4}\, J$. What is the surface tension ?

A square hole of side length $l$ is made at a depth of $h$ and a circular hole of radius $r$ is made at a depth of $4\,h$ from the surface of water in a water tank kept on a horizontal surface. If $l << h,\,r << h$ and the rate of water flow from the holes is the same, then $r$ is equal to

A manometer connected to a closed tap reads $4.5\times10^5\, pascal$. When the tap is opened the reading of the manometer falls to $4\times10^5\, pascal$. Then the velocity of flow of water is ........ $ms^{-1}$

A $U-$ tube in which the cross-sectional area of the limb on the left is one quarter, the limb on the right contains mercury (density $13.6\ g/cm^3$). The level of mercury in the narrow limb is at a distance of $36\ cm$ from the upper end of the tube. What will be the rise in the level of mercury in the right limb if the left limb is filled to the top with water ....... $cm$