# Mass of a material

1. Sep 22, 2008

### chanv1

What mass of a material with density p is required to make a hollow spherical shell having inner radius r1 and outer radius r2?

How do I get the volume of the hollow sphere without any numbers?

Any help would be greatly appreciated!!

2. Sep 22, 2008

### atyy

Give your answer in terms of p, r1 and r2. To start, find the volume of the hollow sphere in terms of r1

3. Sep 22, 2008

### chanv1

I know the volume of a hollow sphere is V = 4/3 pi r^3. But how do I get the answer in terms of p, r1, and r2 without having any given numbers?

4. Sep 22, 2008

### atyy

V = 4/3 pi r^3 is the volume of a sphere, hollow or not.

Give your answer in terms of p, r1, and r2, not in terms of any given numbers (which are not given).

Equivalently, you may treat p, r1 and r2 as your "given numbers".

5. Sep 22, 2008

### Wesli

Your answer won't be an integer, but will contain "r1, and r2." Where you would normally put the numerical value of these unknowns, you leave them as "r1," and "r2."

It also might be more helpful to think of "volume of the hollow sphere," as the "volume of the spherical shell." The volume of a sphere is 4/3πr3, while the volume of a spherical shell is...

6. Sep 28, 2008

### chanv1

Thanks for the help!