A small metal sphere of radius $a$ is falling with a velocity $v$ through a vertical column of a viscous liquid. If the coefficient of viscosity of the liquid is $\eta $ , then the sphere encounters an opposing force of
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According to Stokes’ law, the sphere encounters an opposing force $F$ (or viscous force) when it falls through a viscous liquid of viscosity $\eta $ with a velocity $v$ and it is given by
$f = 6\pi \eta av$
Note : You can also see from the options, only option $(C)$ has the dimensions of force
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