Question

Two drops of same radius are falling through air with steady speed v. If these two drops coalesce and form a big drop, then new terminal speed will be :

• A. V
• B. 2V
• C. 3V
• D. None of these

Answer 1

The correct option is D None of these

$\begin{array}{c}V\\ r\end{array}+\begin{array}{c}V\\ r\end{array}\Rightarrow \begin{array}{c}{V}^{\prime }\\ R\end{array}$

$\frac{4}{3}\pi r^3+\frac{4}{3}\pi r^3=\frac{4}{3}\pi R^3$

$V=\frac{2r^{2}g(s-\sigma )}{9\eta }$

$V^{\prime }=2^{2/3}V$

$V^{\prime }=4^{1/3}V$

Option is (D).