M(r) = mass of gas in a sphere of radius r. Can any particle, Fg=Fcp
GM(r)m
r2
=
mv2
r
GM(r)m=2(K)r ⇒M(r)=
2K
GM
r On differentiating w.r.t r,
dM
dr
=
2K
Gm
.................(1) Here dM = mass of gas in a spherical shell of radius r and thickness dr ∴dM[ρ(r)](dv)=[ρ(r)]4πr2dr....(2) Substitute (2) in (1)