Q. Two rain drops of same radii $'r'$, falling with terminal velocity $'v'$ merge and form a bigger drops of radius $R$. The terminal velocity of the bigger drop is
A) $v\frac{R}{r}$
B) $v\frac{R^{2}}{r^{2}}$
C) $v$
D) $2v$
Explanation
(b) Terminal velocity
$v = \frac{2}{9}\frac{r^{2}(\rho - \sigma)g}{\eta}$
$v\alpha r^{2}$
$\frac{v}{V} = \frac{r^{2}}{R^{2}} \Rightarrow V = \frac{vR^{2}}{r^{2}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.