A rain drop of diameter 1 mm falls with a terminal velocity of $0.7 \mathrm{~ms}^{-1}$ in air. If the coefficient of viscosity of air is $2 \times 10^{-5} \mathrm{Pas}$, the viscous force on the rain drop is

• Correct answer
  A

  $13.2 \times 10^{-8} \mathrm{~N}$
• B

  $6.6 \times 10^{-8} \mathrm{~N}$
• C

  $26.4 \times 10^{-8} \mathrm{~N}$
• D

  $10.4 \times 10^{-8} \mathrm{~N}$

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