🚀 go-pugleaf

I tried subtracting the volume of a sphere without the cell wall from
a sphere with the cell wall to get the cell wall.  

outer radius is 2.0 um/2  = 1.0 um.  volume is 4/3(pie)r * r * r =
3.351 * 10^-17.   I have trouble here converting units.   I don't know
what unit this answer is or how to get it to a useful unit.

inner radius is (2.0 um/2) - 50.0 nm = 1.95 * 10^-6.  Is that right?
Again, what units are we in here?  Anyway, this sphere has volume
4/3(pie)r^3 = 3.1059 * 10^-17.

Subtracting sphere 2 from sphere 1     (3.351 *10^-17) - 3.1059 *
10^-17 = 2.4506 * 10^-18, volume of the cell wall.   I hope.

I'm lost at this point, what units is this in?  How do I get to the
mass in mg?


On Sat, 26 Jan 2008 10:27:07 -0800, Jolt Joltist <joltist@hotmail.com>
wrote:

>I need help with some homework.
>
>Cells can be 2.0 um in diameter and cell wall 50.0 nm thick.  If
>density(mass divided by volume) of the wall material is the same as
>that of water,  what is the mass in mg of the cell wall, assuming the
>cell to be spherical and the wall to be a thin spherical shell?
>
>How do you work this out?