Terminal velocity of a copper ball of radius 5,mm falling through a tank of oil at room temperature

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9-1.Fluid Mechanics

easy

The terminal velocity of a copper ball of radius $5\,mm$ falling through a tank of oil at room temperature is $10\,cm\,s ^{-1}$. If the viscosity of oil at room temperature is $0.9\,kg\,m ^{-1} s ^{-1}$, the viscous drag force is :

A

$8.48 \times 10^{-3}\,N$

B

$8.48 \times 10^{-5}\,N$

C

$4.23 \times 10^{-3}\,N$

D

$4.23 \times 10^{-6}\,N$

(NEET-2022)

Solution

$F\,=6 \pi \eta rv$

$\quad =6 \times 3.14 \times 0.9 \times 5 \times 10^{-3} \times 10 \times 10^{-2}$

$\quad=847.8 \times 10^{-5}\,N$

$\quad=8.48 \times 10^{-3}\,N$

Standard 11

Physics

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