Q. Eight equal drops of water are falling through air with a steady velocity of $10\ {cms}^{- 1}.$ if the drops combine to form a single drop big size, then the terminal velocity of this big drop is
A) $80\ {cms}^{- 1}$
B) $30\ {cms}^{- 1}$
C) $10\ {cms}^{- 1}$
D) $40\ {cms}^{- 1}$
Explanation
(d) $v \propto r^{2}$
$\frac{v_{1}}{v_{2}} = \frac{r_{1}^{2}}{r_{2}^{2}}$
$\frac{10}{v_{2}} = \frac{r^{2}}{8^{2/3}r^{2}} = \frac{1}{4}$
$v_{2} = 40cm/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.