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Estimate the speed of vertically falling raindrops from the following data. Radius of the drops = 0.02 cm, viscosity of air = 1.8 × 10-4 poise, g = 9.9 × 10 m s-2 and density of water = 1000 kg m-3.

Estimate the speed of vertically falling raindrops from the following data. Radius of the drops = 0.02 cm, viscosity of air = 1.8 × 10-4 poise, g = 9.9 × 10 m s-2 and density of water = 1000 kg m-3.

Grade:upto college level

1 Answers

Jitender Pal
askIITians Faculty 365 Points
8 years ago
Sol. To find the terminal velocity of rain drops, the forces acting on the drop are, i) The weight (4/3)π r3 pg downward. ii) Force of buoyancy (4/3)π r3 σg upward. iii) Force of viscosity 6 π η r v upward. Because, σ of air is very small, the force of buoyancy may be neglected. Thus, 6 π η r v = (4/3) πr2 pg or v = 2r2 pg/9η

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