Two drops of same radius are falling through air with steady speed  $\upsilon$. If the two drops coalesce, what would be the terminal speed ?

$$\begin{gathered} V_t=\frac{2r^2(\rho -\sigma )g}{\upsilon n}or{V}_t\alpha r^2 \\ Let R be the radius of bigger drop equating the volumes we have \\ \frac{4}{3}\pi R^3=2\left[\frac{4}{3}\pi r^3\right]\therefore R={\left(2\right)}^{\frac{1}{3}}r \\ Hence, the terminal velocity of big drop V_1={\left(2\right)}^{\frac{2}{3}}v \end{gathered}$$