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Planetary Motion, calculation of orbital period

  • #1
Hi everyone,



I'm really confused with a particular question:

1. 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...

2. Homework Equations

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

3. 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
 

Answers and Replies

  • #2
Dick
Science Advisor
Homework Helper
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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.
 
  • #3
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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