A raindrop of radius 0.2 mm falls through air. If the viscosity of air is 18×10–6Pl, if the viscous drag acting on the drop when its speed is 1ms–1is 67.8×10–p newton, then find p
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Solution
Radius of raindrop, a = 0.2 mm =0.2×10−3m
Air viscosity η=18×10−6Pl
Speed of fall of raindrop, v=1ms−1
From Stokes’ law
Viscous force F=6πηav =6π×18×10−6×0.2×10−3×1 =67.8×10−9N