A rain drop of radius 0.3 mm has a terminal velocity in air 1 ms − 1 . The viscosity of air is 18 × 1 0 − 5 poise. Find the viscous force on the rain drops.

Here, r = 0.3 mm = 0.3 × 1 0 − 3 m , v = 1 ms − 1 η = 18 × 1 0 − 5 poise = 18 × 1 0 − 6 decapoise Viscous force, F = 6 π η rv = 6 × 7 22 × ( 18 × 1 0 − 6 ) × ( 0.3 × 1 0 − 3 ) × 1 = 1.018 × 1 0 − 7 N

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Physics - Fluid Question with Solution | TestHub

PhysicsFluidViscosityMedium2 minPYQ_2018

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A rain drop of radius 0.3 mm has a terminal velocity in air $1 ms^{- 1}$ . The viscosity of air is $18 \times 1 0^{- 5}$ poise. Find the viscous force on the rain drops.

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Solution:

Here, $r = 0.3 mm = 0.3 \times 1 0^{- 3} m, v = 1 ms^{- 1}$ $η = 18 \times 1 0^{- 5}$ poise $= 18 \times 1 0^{- 6}$ decapoise Viscous force, $F = 6 π η rv$ $= 6 \times \frac{22}{7} \times (18 \times 1 0^{- 6}) \times (0.3 \times 1 0^{- 3}) \times 1 = 1.018 \times 1 0^{- 7} N$

Stream:JIPMERSubject:PhysicsTopic:FluidSubtopic:Viscosity

⏱ 2mℹ️ Source: PYQ_2018

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