A rain drop of radius 0.3 mm has a terminal velocity in air 1m/s. the viscosity of air is `18xx10^(-5)` poise. The viscous force on it is-

Options

A. `101.37xx10^(-4)` dyne
B. `101.73xx10^(-2)` dyne
C. `16.95xx10^(-5)` dyne
D. `16.95xx10^(-4)` dyne

Answer

B

Explanation

Given terminal velocity, `v=1ms^(-1)=100cms^(-1)` radius of the raindrop, r=0.3mm `=0.3xx10^(-1)"cm"`
Viscosity of air `eta=18xx10^(-3)"Poise"`
`therefore "Viscous force, F"=6 pi eta rv`
`=1017.36xx10^(-3)"dyne"=101.73xx10^(-2)"dyne"`