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## QuestionPhysicsClass 11

A metal sphere of diameter $$7 cm$$ falls through aliquid of coefficient of viscosity $$0.8 Pa.s$$. When itsvelocity is $$20 cm.s^{-1}$$ the viscous force acting on itis nearly ----$$N.$$
(A) $$0.11$$
(B) $$0.22$$
(C) $$0.3$$
(D) $$0.01$$

Viscous force on the metal sphere = $$6 \pi \eta r V$$
$$= 6 \times \times 0.8 \times \dfrac{3.5}{100} \times \dfrac{4}{3} \pi \left ( \dfrac{3.5}{100} \right )^{3}\times \dfrac{20}{100}N$$
$$= 0.1055 \approx 0.11 N$$