Two drops of water, of diameter $D_1=1mm$ and $D_2=2mm,$ initially $($at $t=0)$ at

$25C$ are allowed to fall in air of $-20C.$ Assuming the lumped capacitance

method valid and freezing to begin when the water reaches $0C,$ which drop will

begin to freeze first? How far will it have fallen? It is safe to assume that the

drops reach their respective terminal fall velocities instantaneously.