# Mass and radius

1. Sep 3, 2008

### unseenoi

1. The problem statement, all variables and given/known data

I know this is a dumb question but if the radius of a planet is one-fifth of the earth's radius. what is the mass of the planet.

Earth mass => 5.97 *1024
earth radius => 6.38 *106

3. The attempt at a solution

my answer: 5.97 *1024(1/10)

Last edited: Sep 3, 2008
2. Sep 3, 2008

### LowlyPion

And incorrect.

If the radius is 1/5 and it has the same density as earth, then what would the mass be?

Think about the ratio of the volume between the 2 and then multiply that appropriately by earth mass.

3. Sep 3, 2008

### unseenoi

Can u please give me more details.

4. Sep 3, 2008

### Banaticus

density = mass/volume --> $\rho=m/v$

What is the formula for determining the volume of a sphere? Given the earth's radius, what is its volume?