Q.

Eight equal drops of water are falling through air with a steady speed of 10 cm/s. If the drops coalesce, the new velocity is  [2023]

1 10 cm/s  
2 40 cm/s  
3 16 cm/s  
4 5 cm/s  

Ans.

(2)

vr2

v1v2=(rR)2

8·43πr3=43πR3

R=2r

10v2=(12)2v2=40 cm/s