The correct option is C 1:32
Given, the ratio of radii of the drops, r1:r2=1:2
The terminal velocity and mass of a body is:
vT=29r2g(σ−ρ)η
where σ is the density of the body i.e rain drop and ρ is density of fluid (air) through which the body is falling.
⇒vT∝r2 ...(i)
Similarly, mass of rain drop will be,
m=σ×43πr3
⇒m∝r3 ...(ii)
From Eq.(i) & (ii),
mvT∝r5
Hence, when rain drops attain vT, the ratio of their momenta will be:
p1p2=m1v1m2v2=(r1r2)5
⇒p1p2=(12)5
∴p1:p2=1:32