Q: Neglecting the density of air, the terminal velocity obtained by a raindrop of radius 0.3 mm falling through the air of viscosity 1.8 × 10^{-5} N/m² will be

(a) 10.9 m/s

(b) 8.3 m/s

(c) 9.2 m/s

(d) 7.6 m/s

Ans: (a)

Sol: Terminal velocity

$ \displaystyle v = \frac{2r^2 (\rho-\sigma)g}{9 \eta} $

$ \displaystyle = \frac{2r^2(\rho -0)}{9 \eta} $