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

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# Homework Help: Distance between 2 planets

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