A raindrop with radius R = 0.2 mm falls from a cloud at a height h = 2000 m above the ground. Assume that the drop is spherical throughout is fall and the force of buoyance may be neglected, then the terminal speed attained by the raindrop is : (Density of water fw = 1000 kg m–3 and density of air fa = 1.2 kg m–3, g = 10 m/s2, Coefficient of viscosity of air = 1.8 × 10–5 Nsm

Engineering

Physics

Viscosity and Terminal Velocity New

Question

A raindrop with radius R = 0.2 mm falls from a cloud at a height h = 2000 m above the ground. Assume that the drop is spherical throughout is fall and the force of buoyance may be neglected, then the terminal speed attained by the raindrop is : (Density of water f_w = 1000 kg m^–3 and density of air f_a = 1.2 kg m^–3, g = 10 m/s², Coefficient of viscosity of air = 1.8 × 10^–5 Nsm^–2)

43.56 ms^–1

14.4 ms^–1

250.6 ms^–1

4.94 ms^–1

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$V_{T} = \frac{2 R^{2} (f_{w} - f_{a}) g}{9 η}$

$= \frac{2 \times {(0 .002)}^{2} \times (1000 - 1 .2) \times 10}{9 \times 1 .8 \times 10^{- 5}} \approx 4 .94$