Question

Calculate the viscous force on a water
drop of radius 0.1 mm falling through air
of n = 1.8*10*-5Kgm-1s-1 with constant velocity 0.15 cm/s​

Answer 1

Here, r=0.1 mm = 0.01cm,

v = 0.15 cm/s  

η = 18 × 10^-5  poise.

According to stokes law, force of viscosity on rain drop is

F = 6πηrv

= 6 × 3.142 × 18 × 10^-5    × 0.01 × 0.15  

= 0.00000509004 dyne = 5.09 × 10^-6 dyne