Question

A rain drop of radius $0.3\text{mm}$ has a terminal velocity in air$=1\text{m/s}.$ The viscocity of air is $8\times {10}^{-5}\text{poise}.$ The viscous force on it is:

• A. $45.2\times {10}^{-4}\text{dyne}$
• B. $101.73\times {10}^{-5}\text{dyne}$
• C. $16.95\times {10}^{-4}\text{dyne}$
• D. $16.95\times {10}^{-5}\text{dyne}$

Answer 1

The correct option is A $45.2\times {10}^{-4}\text{dyne}$

$F=6\pi \eta rv$
$F=6\times 3.14\times (8\times {10}^{-5})\times 0.03\times 100$
$F=4.52\times {10}^{-3}\text{dyne}$