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A raindrop of radius 0.2 mm falls throug...

A raindrop of radius 0.2 mm falls through air: If the viscosity of air is 18 `xx 10^(-6)` Pl, find the viscous drag acting on the drop when its speed is 1 m `s^(-1)`.

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Radius of raindrop,-a- = 0.2 mm
= `0.2 xx 10^(-3)` m
Air viscosity `eta = 18 xx 10^(-6)` PI
Speed of fall of raindrop, v = 1 m `s^(-1)`
From Stokes. law
Viscous force F = `6 pi eta a v`
`6pi xx 18 xx 10^(-6) xx0.2xx10^(-3)xx1`
`67.8xx10^(-9)`N
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