# How to find Density/ Radius of planetesimals

1. Nov 5, 2008

### Cherrio

The ice rich planetesimals that formed the cores of the Jovian planets were about 10 times more massive than Earth. Assuming such an ice ball has a density of 2g cm g-3, what would its radius be? How does this compare to Earth's radius.

I need Help =\

2. Nov 5, 2008

### Kurdt

Staff Emeritus
What have you tried?

3. Nov 5, 2008

### Cherrio

I was thinking of multiplying the Earths mass by 10 then using the fomula m=dv

and use the formula for volume of a sphere to get r? IDK

4. Nov 5, 2008

### Kurdt

Staff Emeritus
Sounds like a good plan.

5. Nov 5, 2008

### Cherrio

okay so that would be m=dv

10 x 5.97 x 1024 Kg which is 5.97x 1025Kg

then convert from Kg to g 1kg= 1000g

5.97x 1025Kg x 1000 g= 5.97x 1028g
volume of a sphere= (4/3) pi r3

5.97x 1028g= (2g cm-3)((4/3)pir3)

im not to sure how to isolate R

6. Nov 5, 2008

### Kurdt

Staff Emeritus
You just need a bit of algebraic manipulation. It might help if you use the letters instead of numbers right until the end.

7. Nov 6, 2008

### Cherrio

ok so it would be

m=d 4/3 pi r3

then m/ d(4/3)pi =r3 ?

then r = cubed root of that anwser?

8. Nov 6, 2008

### Kurdt

Staff Emeritus
Yes, that looks good.