A water drop of $0.01 \mathrm{~cm}^3$ is squeezed between two glass plates and spreads in to area of $10 \mathrm{~cm}^2$. If surface tension of water is 70 dyne $/ \mathrm{cm}$ then the normal force required to separate glass plates from each other will be

' $n$ ' small water drops of same size (radius $r$ ) fall through air with constant velocity V. They coalesce to form a big drop of radius R . The terminal velocity of the big drop is

A small metal sphere of density $\rho$ is dropped from height $h$ into a jar containing liquid of density $\sigma(\sigma>\rho)$. The maximum depth up to which the sphere sinks is (Neglect damping forces)

Water is flowing steadily in a river. A and B are the two layers of water at heights 40 cm and 90 cm from the bottom. The velocity of the layer A is $12 \mathrm{~cm} / \mathrm{s}$. The velocity of the layer B is