1. Basically it tells me that Mars has a mass of 8*10^23kg.Phobos, its closest moon, whips around planet in 7 hrs. How far from Mars is Phobos?(adsbygoogle = window.adsbygoogle || []).push({});

I got that m=8*10^23 and T= 7 hrs . I am pretty sure i need to find the radius.

my only problem is that I cant find the formula where i can figure out r by using mass and T.

What am i doin wrong? Whats the formula that i need?

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

2. Relevant equations

3. The attempt at a solution

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Distance between 2 planets

**Physics Forums | Science Articles, Homework Help, Discussion**