Discussion Forum



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) 45.2×10−4dyne

B) 101.73×10−5 dyne

C) 16.95×10−4 dyne

D) 16.95×10−5dyne

Answer:

Option A

Explanation:

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