# Thread: need help - spherical coordinates

1. ## need help - spherical coordinates

I have really no idea how to define the rho, theta, and phi limits for this question. Please help!!

Suppose that the density at a point in a gaseous spherical star is modeled by the formula
delta = deltasub0 times e^ -(rho/R)^3

where deltasub0 is a positive constant, R is the radius of the star, and rho is the distance from the point to the star's center . Find the mass of the star.

2. You'll need the Jacobian for that. Something about $\rho^{2}\sin(\phi)$ ringing a bell?

You're just filling up a sphere.

$\rho\;is\;[0,R]$

$\theta\;is\;[0,2\pi]$

$\phi$ is -- Oh, you do that one.

3. Hi TKHunny,

I have not yet learnt Jacobian.

Can you only use the idea of spherical coordinates to find the rho, phi, and theta ?

with the spherical coordinates ideas:
um, since it is a gaseous SPHERICAL STAR, i guess the theta should be from 0 to 2pi.

since R is the radius of the star, I guess rho is from 0 to R.

For phi, I am not sure. I know phi is restricted from 0 to pi.
I guess phi is from 0 to pi. (purely a guess! )
If you know the reason , please tell me why. Thank you very much.