Question

eight identical droplets of the same mass and radius falling down with a terminal speed for centimetre per second c o a l e s c e to form a single drop what will be the terminal speed of the c o a l e s c e drop

Answer 1

I can't see how any of those answers works. The terminal velocity (ignoring buoyancy) is proportionate to the square root of m/A, where m is mass and A is the projected area, assuming constancy of density of air, coefficient of drag (is assume the coalesced drop is also spherical), and gravitational field strength.

As the mass of the coalesced drop is 8 times the individual drops, and area is 4 times the individual drops, the terminal v should increase over the individual drops by a factor of sqrt(8/4), i.e. sqrt(2), resulting in a terminal v of approx 8.5 cm/s.

Also query why this question is framed using cm per second rather than the SI unit of metres per second?

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