Volume rate flow of a liquid of density $\rho$ and coefficient of viscosity $\eta$ through a cylindrical tube of diameter $D$ is $Q.$ Reynold's number of the flow is

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

A spherical air cavity of radius $R$ is inside a liquid of uniform density $\rho$ and surface tension $T$ as shown in the figure. The excess pressure inside the cavity is $\left(P_1\right.$ is the pressure inside and $P_2$ is the pressure outside the cavity)