Eight equal drops of water are falling through air with a steady speed of $10 \mathrm{cm}/\mathrm{s}$. If the drops coalesce, the new steady speed is

Terminal velocity, $\mathrm{v}=\frac{2}{9\mathrm{\eta }}(\mathrm{\rho }-\mathrm{\sigma }){\mathrm{r}}^2\mathrm{g}\Rightarrow \mathrm{v}\propto {\mathrm{r}}^2$
When eight drops combine, the final radius is 2 times that of each drop
Since radius has doubled, velocity becomes 4 times.