Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Kepler's 3rd law to determine mass of jupiter

  1. Dec 6, 2008 #1
    my problem involves creating a graph of log10(a) vs log10(P) and to calculate the mass of jupiter from the graph.

    I have created the graph and it seems to be right since the of the trend line is 3/2. My problem is that I am unsure how to go about calculating the mass from the graph.

    I used the orbital period and length of the semi-major axis of the Galilean satellites and 3 others to get the equation y = 1.5012x - 8.1973

    I have tried using m1+m2= (4*P^2*a^3)/(G*P^2), though that produced a rather large value and doesn't utilize the graph at all.

    Any help or nudges in the right direction would be greatly appreciated, Thanks!
     
  2. jcsd
  3. Dec 6, 2008 #2

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    You might try posting this same question in the Homework Questions section of PF
    https://www.physicsforums.com/forumdisplay.php?f=153

    They are good at giving nudges without actually doing the problem for you.

    It looks to me as if you have a typo or misprint in your equation. You wrote a P instead of a Pi (the number 3.14...)
    at one point.

    m1+m2= (4*P^2*a^3)/(G*P^2)

    Better check in your textbook or your notes from class. A plain letter P would stand for the period.
    On the other hand Pi^2 is a number roughly about equal to 10. So 4*Pi^2 is roughly about 40.
    Once you check to make sure you don't have any major misprints like that, then if you need help
    you could see what you can learn at the PF Homework forum.
     
    Last edited: Dec 6, 2008
  4. Dec 6, 2008 #3
    thanks for the input - it is actually P, being the period, in my equation, not Pi. I hadn't realized that I had posted in the wrong area.
     
  5. Dec 6, 2008 #4

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    Seriously, you need to check your equation in the textbook or the class notes.
    In the way you have written it, you have P^2 both in the numerator and in the denominator.
    In one case that is correct, it is supposed to be the period squared.
    In another case it is not correct---where you have written P^2 you should have written Pi^2.

    The Kepler law equation, as usually written, has a pi^2 in it, and what you have written does not. So it looks to me like you have screwed up the equation. Better check.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Kepler's 3rd law to determine mass of jupiter
  1. Kepler's law (Replies: 3)

  2. Kepler Law (Replies: 2)

Loading...