Question

What will be the approximate terminal velocity of a rain drop of diameter 1.2 x l0^-3 m, when density of rainwater ≈ l0³ kgm^-3 and the co-efficient of viscosity of air ≈ 1.8 x l 0^-5 Nsm^-2? 

Options

• 4.36 ms^-1

• 43.6 ms^-1

• 392 ms^-1

• 436 ms^-1

Answer 1

43.6 ms^-1

Explanation:

`6pieta"r""v" = 4/3 pi"r"^2 "pg"`

`therefore "v" = 2/(9eta) "r"^2"pg"`

`therefore "v" = (2 xx 0.6^2 xx 10^(- 6) xx l0^3 xx 9.8)/ (9 xx l.8 xx 10^-5)`

= 43.6 ms^-1