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NEET 2022
Exam
NEET
Year
2022
Subject
Physics
Chapter
Mechanical Properties of Fluids

NEET 2022 · Physics · Mechanical Properties of Fluids

The terminal velocity of a copper ball of radius 5 ~mm falling...

The terminal velocity of a copper ball of radius 5 mm5 \mathrm{~mm} falling through a tank of oil at room temperature is 10 cm s−110 \mathrm{~cm} \mathrm{~s}^{-1}. If the viscosity of oil at room temperature is 0.9 kg m−1 s−10.9 \mathrm{~kg} \mathrm{~m}^{-1} \mathrm{~s}^{-1}, the viscous drag force is:

Options

  1. A8.48×10−3 N8.48 \times 10^{-3} \mathrm{~N}
  2. B8.48×10−5 N8.48 \times 10^{-5} \mathrm{~N}
  3. C4.23×10−3 N4.23 \times 10^{-3} \mathrm{~N}
  4. D4.23×10−6 N4.23 \times 10^{-6} \mathrm{~N}

Correct answer

A. 8.48×10−3 N8.48 \times 10^{-3} \mathrm{~N}

Step-by-step solution

By Stobal's law, F=6πηrv\mathrm{F}=6 \pi \eta r v (where, the symbols have their usual meanings) F=6×3.14×0.9×5×10−3×10×10−2 F=84.78×10−4=8.478×10−3 N=8.48×10−3 N\begin{aligned} \mathrm{F} & =6 \times 3.14 \times 0.9 \times 5 \times 10^{-3} \times 10 \times 10^{-2} \\ \mathrm{~F} & =84.78 \times 10^{-4} \\ & =8.478 \times 10^{-3} \mathrm{~N}=8.48 \times 10^{-3} \mathrm{~N} \end{aligned}
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