Mean densities exam prep help please?

Question

I have two planetary objects as follows below, but how do i calculate the mean densities of each body and show it in the correct format and check my answers?

object a) mean radius/lm 1738 , mass/10^20kg 735 , volume/10^18cm^3 22.0

object b) mean radius/lm 718 , mass/10^20kg 16 , volume/10^18cm^3 1.6

Its mean radius i do apologise i copy pasted and editted lol my bad

Answer 1

The mean density is the mass divided by the volume.

I'm a little puzzled by your data. What is meant by "mean radius/lm"? If I solve for the radius given that the volume is 22 × 10^18 cm³, I get 1.738 × 10^6 cm, which is 1.738 × 10^4 m or 17.38 km -- a small asteroid. But then the density is 3.34 × 10^6 g/cm³. The densest element has a density of only about 23 g/cm³. I suspect that the given volumes are in m³, not cm³.

Then the mean density of the first object would be 3.34 × 10³ kg/m³, a reasonable value, and the mean radius would be 1738 km, a reasonable value (it is in fact the radius of Earth's moon; and the given mass is that of the moon. See http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html )