Q149 / 150 · MHT CET 2012 · Physics

A solid ball of volume $V$ is dropped in a viscous liquid. It experiences a viscous force $F$. If the solid ball of volume $2 V$ of same material is dropped in the same fluid, then the viscous force acting on it will be

  • A
    $n F / 2$
  • B
    $\mathrm{F} / \mathrm{2}$
  • Correct answer
    C
    $2 F$
  • D
    $2 n F$

Solution

Viscous force, $F=6 \pi \eta r v$ but $$ v \propto r^{2} $$ $$ \therefore \quad \begin{array}{lll} F \propto V & \text { (volume) } \end{array} $$ So, on doubling the volume of the ball, the viscous force is doubled.

Hence, the correct answer is option: 'C'.

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