Kepler's Third Law: Homewor Help

AI Thread Summary
A spy satellite located one Earth radius above the surface has a calculated period of revolution of 1.5 x 10^4 seconds. The discussion revolves around applying Kepler's Third Law, specifically the equation k = T^2/R^3, to determine the period. Participants suggest using Newton's law of gravitation to express the gravitational force in terms of g. There is a focus on clarifying the appropriate constant for the calculation, as well as the need for a reference period when not using the Moon. The conversation emphasizes the importance of understanding the relationship between gravitational forces and orbital motion.
No2
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Homework Statement



A spy satellite is located one Earth radius above the surface of the Earth. What is its period of revolution?

ans. 1.5 x 10^4 s

Homework Equations



I'm trying to use the kepler's constant: k = T^2/R^3

The Attempt at a Solution

 
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Kepler's law can be derived by equating the force of attraction with centripetal force

i.e. GMm/r2=mω2r

or GM/r3=(2π/T)2

So what would be your constant or proportionality 'k' if you rearrange to get T2/r3?
 
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Hi No2! Welcome to PF! :smile:

(try using the X2 icon just above the Reply box :wink:)
No2 said:
I'm trying to use the kepler's constant: k = T^2/R^3

Unless you're using the Moon, what T are you going to compare with? :confused:

Use the ordinary Newton's law of gravitation to find the force of gravity as a multiple of g (that's our g, not G ! :wink:), and https://www.physicsforums.com/library.php?do=view_item&itemid=27" :smile:
 
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