Question

A rain drop of radius $0.3mm$ has a terminal velocity in air $1m/s$. The viscosity of air is $18\times {10}^{-5}$ poise. The viscous force on it is

• A. $101.73\times {10}^{-4}dyne$
• B. $101.73\times {10}^{-5}dyne$
• C. $16.95\times {10}^{-5}dyne$
• D. $16.95\times {10}^{-4}dyne$

Answer 1

The correct option is A $101.73\times {10}^{-4}dyne$

Given Data:-

$r=0.3mm=0.03cm$

${}_V=1m/s=100cm/s$

$\eta =18\times {10}^{-5}poise$

$F=?$ $dyne$

The formula required is:-

$F=6\pi \eta r_V$

$\therefore F=6\times 3.14\times 18\times {10}^{-5}\times 0.03\times 100=101.73\times {10}^{-4}$

$Answer=101.73\times {10}^{-4}dynes$