The velocity of upper layer of water in a river is $36 kmh ^{-1}$. Shearing stress between horizontal layers of water is $10^{-3} Nm ^{-2}$. Depth of the river is $m$. (Co-efficiency of viscosity of water is $10^{-2} \,Pa . s$ )
JEE MAIN 2022, Medium
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$F =\eta A \frac{\Delta v _{ x }}{\Delta y }$
$\frac{ F }{ A }=\eta \frac{\Delta v _{ x }}{\Delta y }$
$\Rightarrow 10^{-3}=10^{-2} \times \frac{36 \times 1000}{ h \times 3600}$
$\Rightarrow h =10^{-2} \times \frac{36 \times 1000}{10^{-3} \times 3600}=100 \,m$
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