The height of mercury in the barometer tube is $70 \mathrm{cm}$ due to entrapped air in it as shown in figure. Now from this position tube is pulled up slightly, then length of the mercury column in the tube will

An incompressible liquid is flowing through a horizontal pipe as shown in figure. The magnitude of velocity $v$ is

A container filled with a liquid of density $4\rho$ as shown in the figure. The velocity of efflux through orifice is ( $\rho$ is density of water and $\mathrm{g}=10{ \mathrm{m} \mathrm{s}}^{-2}$)

An ideal liquid is flowing through the horizontal tube as shown in figure. If areas of cross-section of end $A$ and $B$ are $2{ \mathrm{mm}}^2$ and $4{ \mathrm{mm}}^2$ respectively and velocity of liquid at end $A$ is $4 \mathrm{m} {\mathrm{s}}^{-1}$ then velocity of liquid at end $B$ will be