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} $