Re: Mass of star

This sounds like a homework problem, so I will just
give some hints. You can solve the first equation for
M(r) and plug this into the second equation. Then you
have one equation for P(r). Solve this equation.

Ulf Torkelsson

NILS BÖRJESSON wrote:
> I have posted about this before, both to sci.physics
> and sci.math, but I didn't get any answers,
> so i decided that i should try this more serios group.
>
> Also I appoliges for my poor english.
>
> Here is the question:
> Suppose you have a star with constant temperature in
> the whole volym, and that boyles law holds for the gas.
>
> Let P(r) bee the pressure at distance r from the stars
> center of mass.
> And M(r) the mass out to r from the center of mass.
>
> THEN:
> P'(r)=-P(r)M(r)/r^2
> M'(r)=P(r).r^2
>
> And M(0)=0
>
> I have choicen the units to make the equation look good.
> What is the limit of M(r) as r go to infinity.
> It' seems like it must go to infinity.
> Can somone prove this?
>
>

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