# Mass of star problem

1. Mar 2, 2014

### jimmyd

hi, this is my first post here as i have driven insane by a math problem for my final year astronomy class, ive been at it for 3 hours and i can't make sense of it

is the question even correct as i have made the assumption that the volume of a sphere times the density would give me 4 were there is a 2 and the density p instead of the density constant pc?

2. Mar 2, 2014

### SteamKing

Staff Emeritus
The density of the star is not constant throughout its volume. The expression for the density in section (1a) should be written

ρ(r) = ρ$_{c}$(1 - (r/R)$^{3}$)

for clarity. In order to derive M(r) and the total mass, you must do some integrations.