# Astronomic gravitation problems

1. If the INternational space station has an orbital velocity of 9,000 m/s. find the time (in minutes) it takes to make one complete orbit.

Relevant equations
F = mv2/ R = m4[pi]2R / T2

The attempt at a solution
Is this the way to solve for T?
Do I use earth mass and Earth R b/c that all the question says?

2. A martian day is 1.03 earth days. At what altitude above Mars should a communications satelite be placed such that it always stay over the same spot above the surface of mars (answer in units of miles. 1000m = 0.62 miles

Relevant equations
F = ma = m4[pi]2R / T2
a= GM/R2

The attempt at a solution
I know how to solve the problem but what kinda threw me off are the martian days given...
Is T 354.36 days that is 365/1.03
If it is, can i find "a" after the "m" cancel, than solve for R which is (mar's radius + mars altitude)

3. find the lagrange Point between the sun and Jupiter. In between what two planets will you find this point?

Jupiter:
mass: 1.9x1027 kg

Sun:
mass: 1.99x1030

distance betwwen sun and Jupiter: 778x106 km

Relevant equations
Im really not sure what is lagrange point equation, is it... GMsunmjupiter/ r
r is the distance of Jupiter- sun ?

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LowlyPion
Homework Helper
You have the velocity and and hence you have

mv²/r = Gravitational force = GMm/r²

This yields v² = GM/r

What you don't know from that equation is r. But you want to calculate it, because v/r = ω

and ω = 2πf = 2π/T or

T = 2π/ω = 2πr/v