Homework Help: Finding mass of black hole once given the density

1. May 2, 2012

fifel85

1. The problem statement, all variables and given/known data
Calculate the mass and radius of a black hole with density 750 kg/m^3.

2. Relevant equations

3. The attempt at a solution
In a previous question, I already used the Schwarzchild radius to come up with a formula for the density of a black hole:
D = (mass/(4/3pi((2Gmass/c^2)^3). I realize that this should be enough to solve for mass, but I am having difficulty with the algebra...How do I solve for mass when one of the "mass" variables is stuck inside the Scharzchild radius in a complicated fraction?

2. May 2, 2012

George Jones

Staff Emeritus
Apply the ^3 to everything inside the brackets to which it is attached.