Question

Find the terminal velocity of a rain drop of radius 0.01 mm. The coefficient o viscosity of air $1.8x{10}^{-5}N-s/m^2$ and its density is 1.2 kg/$m^3$. Density of water=1000 kg/$m^3$.$Takeg=10m/s^{-2}\left(Forceofbuoyancyduetoairisneglected\right)$

• A. $0.2m/sec$
• B. $0.02m/sec$
• C. $0.12m/sec$
• D. $0.012m/sec$

Answer 1

The correct option is D $0.012m/sec$

$\text{we know}$

$\text{fnet}=\text{drag force.}$

$({\rho }_w-{\rho }_n)vg=6\pi nvr$

$\left(998.8\right)\frac{4}{3}\pi \times {10}^{-15}\times 10=6\pi \times 1.8\times {10}^{-5}\times v\times {10}^{-5}$

$V=\frac{998.8\times 4\times {10}^{-4}}{18\times 1.8}=120\times {10}^{-4}$

$=0.012m/s$

Answer:- (D)