1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Need help with keplers 3rd law of periods problem

  1. Apr 2, 2008 #1
    [SOLVED] need help with keplers 3rd law of periods problem

    1. The problem statement, all variables and given/known data
    A 20 kg satellite has a circular orbit with a period of 2.6 h and a radius of 9.4E6 m around a planet of unknown mass. If the magnitude of the gravitational acceleration on the surface of the planet is 8.6 m/s2, what is the radius of the planet?



    2. Relevant equations
    T^2=((4pi^2)/(GM))r^3

    a gravity=(GM)/r^2


    3. The attempt at a solution

    I used the law of periods to find the mass and then used the second equation to find the radius of the planet but I got a really small number
     
  2. jcsd
  3. Apr 2, 2008 #2

    hage567

    User Avatar
    Homework Helper

    Can you show your calculations in more detail? Note that r in your first equation is not the same as r in the second (in case you forgot that).
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook