JEECUP (UP Polytechnic) Stokes' Law — practice questions

Explore 2 free Stokes' Law questions in JEECUP (UP Polytechnic) Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Stokes' Law questions and exercises with answers

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**Stokes' law** gives the viscous drag on a small sphere of radius $r$ moving with velocity $v$ through a fluid of viscosity $\eta$ as:Read the answer and worked solution →A steel ball of radius 0.3 mm falls at 2 m/s through glycerine ($\eta = 0.833$ N·s/m²). The viscous drag is:Read the answer and worked solution →

Worked practice questions

Stokes' law gives the viscous drag on a small sphere of radius $r$ moving with velocity $v$ through a fluid of viscosity $\eta$ as:

$F_v = 6\pi \eta r v$
$F_v = \pi \eta r v$
$F_v = 6\pi \eta r^2 v$
$F_v = \eta r v / 6\pi$

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Correct answer: A. $F_v = 6\pi \eta r v$

$F_v = 6\pi \eta r v$. Valid for laminar flow at low Reynolds number. Used to derive terminal velocity of a sphere falling in a fluid.

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A steel ball of radius 0.3 mm falls at 2 m/s through glycerine ($\eta = 0.833$ N·s/m²). The viscous drag is:

$9.4 \times 10^{-3}$ N
$9.4 \times 10^{-5}$ N
$0.094$ N
$1.5 \times 10^{-3}$ N

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Correct answer: A. $9.4 \times 10^{-3}$ N

$F = 6\pi\eta r v = 6 \times 3.142 \times 0.833 \times 0.3 \times 10^{-3} \times 2 \approx 9.42 \times 10^{-3}$ N.