Q.

Small water droplets of radius 0.01 mm are formed in the upper atmosphere and falling with a terminal velocity of 10 cm/s. Due to condensation, if 8 such droplets are coalesced and formed a larger drop, the new terminal velocity will be _______ cm/s.                    [2024]


Ans.

(40)            m=mass of small drop, M=mass of bigger drop

                 Vt=29r2(ρ-σ)gηVtr2

                 8m=M8r3=R3R=2r

                 Radius double so Vt becomes 4 times:

                  Vt=4×10=40cm/s