Gujarati
Hindi
9-1.Fluid Mechanics
normal

A spherical solid ball of volume $V$ is made of a material of density $\rho _1$. It is falling through a liquid of density $\rho _2(\rho _2 < \rho _1)$. Assume that the liquid applies a viscous force on the ball that is proportional to the square of its speed $v,$ i.e., $F_{viscous} = -k\upsilon ^2 (k > 0)$. The terminal speed of the ball is

A

$\sqrt {\frac{{Vg({\rho _1} - {\rho _2})}}{k}} $

B

$\frac{{Vg{\rho _1}}}{k}$

C

$\sqrt {\frac{{Vg{\rho _1}}}{k}} $

D

$\frac{{Vg({\rho _1} - {\rho _2})}}{k}$

Solution

The force acting on the ball are gravity force. buoyancy force and viscous force. When ball acquires terminal speed. it is in dynamic equilibrium, let terminal speed of ball is $v_{T}$

So. $\mathrm{V} \rho_{2} \mathrm{g}+\mathrm{kv}_{\mathrm{T}}^{2}=\mathrm{V} \rho_{1} \mathrm{g}$

$v_{T}=\sqrt{\frac{V\left(\rho_{1}-\rho_{2}\right) g}{k}}$

Standard 11
Physics

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