1) A raindrop of radius 0.3 mm has a terminal velocity in air is 1 m/s. The viscosity of air is 8 x 10-5 poise. The viscous force on it is A) $45.2\times 10^{-4}$dyne B) $101.73\times 10^{-5}$ dyne C) $16.95\times 10^{-4}$ dyne D) $16.95\times 10^{-5}$dyne Answer: Option AExplanation:Radius of drop, r = 0.3 mm = 0.03 cm Terminal velocity v = 1 m/s = 100 cm/sec Viscosity of air, η = 8 x 10-5 poise Viscous force, f = 6 πηrv F = 6 x 3.14 × (8 ×10-5) x 0.03 x 100 = 4.52 x10-3 dyne
