Find the terminal velocity of a rain drop of radius 0.01 mm. The coefficient of viscosity of air is `1.8xx10^-5 N-sm^-2` and its density is `1.2kgm^-3`.Density of water `=1000kgm^-3`. ` Take g=10ms^-2`

Explanation

The fores on the rain drop are
a. the weight `4/3pir^3rhog` downward,
b. the force of buoyancy `4/3pir^3 sigmag` upward,
c. the force of viscosity `6pietarv` upward.
Here `rho` is density of water and `sigma` is the density of air. At termiN/Al velocity the net force is zero. As the density of air is much smaller than the density of water, thus, at termiN/Al velocity
6pietarv=4/3pir^3rhog`
or `v=(2r^2rhog)/(9eta)`
`=(2xx(0.01mm)^2x(1000kgm^-3)(10ms^-2))/(9xx(1.8x10^-5N-sm^I-2))`
`=1.2cms^-2`