The terminal velocity of a rain drop is `30cm//s`. If the viscosity of air is `1.8xx10^(-5)Nsm^(-2)`.The radius of rain drop is

Options

A. `1mum`
B. `0.5mm`
C. `0.05mm`
D. `1mm`

Answer

C

Explanation

`v_(f) =(2)/(9) (r^(2)(rho-sigma)g)/(eta)`
Igonoring the density f air `sigma` we have,
`v_(T) = (2)/(9) (r^(2)rhog)/(eta)`
`:. R = sqrt((9etav_(T))/(2hog))`
`=sqrt((9xx1.8 xx 10^(-5)xx0.3)/(2xx10^(3)x9.8))`
`= 0.49 xx 10^(-4)m`
`~~ 0.05 mm`