The Martian satellite Phobos travels in an approx circular orbit with r=9.4*10^6 meters and period 7h 39min. Find the mass of mars.(adsbygoogle = window.adsbygoogle || []).push({});

I am supposed to use the concept of gravitational F=centripital force[tex]=m\frac{v^2}{r}[/tex] and the fact that [tex]v=\frac{2\pi r}{T}[/tex]

so this is my attempt:

[tex]F_g=\frac{GMm}{r^2}=m(\frac{v^2}{r})[/tex]

implies [tex]\frac{GMm}{r^2}=\frac{m4\pi^2r}{T^2}[/tex]

implies [tex]M=\frac{4\pi^2r}{GT^2}[/tex]

Should this not work? or am I just putting these numbers into my calculator wrong. I have T in seconds=275405

Text says it is 6.5*10^23 kg

Casey

ps I am more concerned with learning the method here.

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# Homework Help: Find the Mass of Mars

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