The terminal velocity of a copper ball of radius $2.0 \;mm$ falling through a tank of oll at $20\,^{\circ} C$ is $6.5 \;cm s ^{-1} .$ Compute the viscosity of the oil at $20\,^{\circ} C .$ Density of oil is $1.5 \times 10^{3} \;kg m ^{-3},$ density of copper is $8.9 \times 10^{3} \;kg m ^{-3}$

  • A

    $1.1 \times 10^{-1} kg m ^{-1} s ^{-1}$

  • B

    $9.9 \times 10^{-1} kg m ^{-1} s ^{-1}$

  • C

    $6.37 \times 10^{-2} kg m ^{-1} s ^{-1}$

  • D

    $5.98 \times 10^{-1} kg m ^{-3} s ^{-1}$

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