Why does velocity increase when water flowing in broader pipe enters a narrow pipe?

 Find the pressure $200 \mathrm{m}$ below the surface of the ocean if pressure on the free surface of liquid is one atmosphere.

Density of sea water $= 1060 \mathrm{kg}/{\mathrm{m}}^3$ , $g=9.8 m/s^2$

Calculate the viscous force acting on a rain drop of diameter $1 \mathrm{mm}$, falling with a uniform velocity $2 \mathrm{m}/\mathrm{s}$ through air. The coefficient of viscosity of air is 

$1.8\times {10}^{-5}\mathrm{Ns}/{\mathrm{m}}^2$