# Physics Newb Needs Help With Mass!

1. Feb 23, 2005

### R.J.

First of all ... GREAT SITE!

I really stink horribly at physics and I am stuck on the following problem:
How do you find the mass of the moon from the following information:
Density: 3.36g/cm2
Diameter: 2160 Miles

I am figuring that the diameter should be 1/2 to 1080 to obtain the radius.
Then I tried using the formula
4/3 x 3.14 x r^3
To obtain volume. But it is there that I am stuck.

Any help would be greatly appreciated.

Thanks!
RJ

2. Feb 23, 2005

### ToxicBug

First of all, isn't the density supposed to be in cubic centimeters? Also, make sure you convert everything to meters, otherwise your equations might not work.

3. Feb 23, 2005

### R.J.

Yes, I typed incorrectly. It should have been cm3.

Any help on a formula?

4. Feb 23, 2005

### Justin Lazear

What're you stuck with? You just plug in 1080 miles into the formula for r.

I would suggest first converting miles to meters or to cm, so that you have common units.

--J

5. Feb 24, 2005

### stunner5000pt

Look at the units of density 3.36g/cm^3. What are grams the units of? What are centimetres the units of?? Now density is given by the ratio of these two quantities right??
Since you know the density, and the volume, you can now find the mass

OH and convert your miles and centimetres to metres and grams to kilograms