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Question: Answered & Verified by Expert
A small ball of mass $m$ and density $\rho$ is dropped in a viscous liquid of density $\rho_0$. After sometime, the ball falls with constant velocity. The viscous force on the ball is :
PhysicsMechanical Properties of FluidsJEE MainJEE Main 2024 (06 Apr Shift 1)
Options:
  • A $m g\left(1-\rho \rho_0\right)$
  • B $m g\left(1+\frac{\rho}{\rho_0}\right)$
  • C $m g\left(\frac{\rho_0}{\rho}-1\right)$
  • D $m g\left(1-\frac{\rho_0}{\rho}\right)_{\nabla}$
Solution:
2783 Upvotes Verified Answer
The correct answer is: $m g\left(1-\frac{\rho_0}{\rho}\right)_{\nabla}$
$\mathrm{mg}-\mathrm{F}_{\mathrm{B}}-\mathrm{F}_{\mathrm{v}}=\mathrm{ma}$
$\mathrm{a}=0$ for constant velocity
$\begin{aligned}
& m g-F_B=F_v \\
& F_v=m g-v \rho_0 g=m g-\frac{m}{\rho} \rho_0 g=m g\left(1-\frac{\rho_0}{\rho}\right)
\end{aligned}$

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