A rain drop of radius 0.3 mm has a terminal velocity in air 1 ms -1. The viscosity of air is 18 × 10-5 poise. Find the viscous force on the rain drops.

Question

A rain drop of radius 0.3 mm has a terminal velocity in air 1 ms -1. The viscosity of air is 18 × 10-5 poise. Find the viscous force on the rain drops. (A) 5.02 × 10-7 N (B) 1.018 × 10-7 N (C) 1.05 × 10-7 N (D) 2.058 × 10-7 N

Tardigrade Admin · Accepted Answer

Given, r=0.3 mm =0.3 × 10-3 m , v=1 ms -1 η=18 × 10-5 poise =18 × 10-6 decapoise Viscous force, F=6 π η r v =6 × (22/7) ×(18 × 10-6) ×(0.3 × 10-3) × 1 =1.018 × 10-7 N

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

$5.02 \times 1 0^{- 7} N$

$1.018 \times 1 0^{- 7} N$

$1.05 \times 1 0^{- 7} N$

$2.058 \times 1 0^{- 7} N$

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

Q. A rain drop of radius 0.3mm has a terminal velocity in air 1ms−1. The viscosity of air is 18×10−5 poise. Find the viscous force on the rain drops.

5.02×10−7N

1.018×10−7N

1.05×10−7N

2.058×10−7N