How do you estimate the mass of a nucleus?

[erinec]

Homework Statement

Estimate the mass of a nucleus with a radius of 2.80 * 10^-15m.

Homework Equations

I do not know if there is an 'equation' for this.

The Attempt at a Solution

The answer is 2.11*10^-26.. but I don't even know how to approach this question.

 

[LowlyPion]

I'd start with the radius of a proton - .857 fm (femtometer) and its mass 1.67*10^-27 kg then figure the volume of the 2.8 fm volume they want you to fill.

http://en.wikipedia.org/wiki/Proton