Planetary Motion, calculation of orbital period

AI Thread Summary
The discussion centers on calculating the orbital period of a space shuttle orbiting Earth at a specific distance. The gravitational field strength is given as 8.9 N/kg, and the participant is confused about using two different equations for the calculation. It is clarified that while the equation r^3/T^2 is a constant for objects orbiting a particular mass, it is not equivalent to gravitational field strength (g) and lacks the correct dimensions. The correct approach involves using the equation g = 4π²R/T² for accurate results. Understanding the distinction between these formulas is crucial for solving orbital period problems correctly.
Stevo_evo_22
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Hi everyone,



I'm really confused with a particular question:

Homework Statement






A space shuttle orbits the Earth at 6720 km from its centre. The gravitational field strength is 8.9N/kg. Calculate the shuttle's orbital period in minutes...

Homework Equations



g=4pi^2 x R /T^2

The Attempt at a Solution


The thing is, I know how to solve it using g=4pi^2 x R /T^2, but I want to know why I can't just use g=r^3/T^2 (the constant for all objects orbiting a particular mass)...if I have r and g, why can't i just use this equation?

Thanks!

Steve
 
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Because r^3/T^2 is a constant. But that constant isn't the same as g. It doesn't even have the right dimensions.
 
Dick said:
Because r^3/T^2 is a constant. But that constant isn't the same as g. It doesn't even have the right dimensions.

ahh ok...thanks :)
 

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