Determining Orbital Period of a Planet

  • #1
Using the equation P2 = (4 * pi2 * a3)/(G(M+m)) to find the orbital period of Earth where:

P = orbital period
a = semi-major axis = 1.50e11 m
G = 6.67e-11 m3 kg-1 s-2
M = mass of sun (in this case) = 1.989e30 kg
m = mass of Earth = 5.972e24 kg

I have been trying to find the orbital period of the Earth but the answers I've been getting make no sense.

P2 = (4 * pi2 * (1.50e11)3) / (G(1.989e30 + 5.972e24))

P = 31690989.27

What are the units on P? I tried following the units as they cancelled each other and I ended up with s kg-2. Any advice would be helpful.

Thanks!

- Marcin
 

Answers and Replies

  • #2
lewando
Homework Helper
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P has units of seconds.
 
  • #3
Bandersnatch
Science Advisor
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Hello Marcin

Try calculating how many seconds there are in a year. And compare with your answer.
 
  • #4
Ah yes. Well that was embarrassing. Thank you Bandersnatch!
 

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