1. Not finding help here? Sign up for a free 30min 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!

Radius of orbit?

  1. Aug 4, 2005 #1
    A satellite circles planet Zeron every 98 min. The mass of the planet is known to be 5.0 x 10^4 kg. What is the radius of the orbit?

    I don't know what I'm doing wrong, Im using the formula T^2=(4(pi)^2/GM)r^3.......and Im not coming up w/ the right answer, I have like 5 choices to choose from and theire all x10^6...
     
  2. jcsd
  3. Aug 4, 2005 #2

    Astronuc

    User Avatar

    Staff: Mentor

    Balance centripetal force with gravitational force - both are proportional to the mass of the satellite.

    Remember the angular frequency, [itex]\omega[/itex] = 2[itex]\pi[/itex]/T, where T is the period.

    And tangential speed, v = [itex]\omega[/itex]r
     
  4. Aug 4, 2005 #3

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    did you convert the period (T) to seconds?
     
  5. Aug 4, 2005 #4
    I tried converting it to seconds and leaving it in minutes...still the answer is way off.
     
  6. Aug 4, 2005 #5

    Doc Al

    User Avatar

    Staff: Mentor

    That's an awfully tiny planet. Are you sure of that number?
     
  7. Aug 4, 2005 #6
    Yep, thats what it says in the problem. Are we supposed to use Kepler's third law or whatever to solve this? It seems really easy that way, but when you plug in the numbers, it just doesn't work out.
     
  8. Aug 4, 2005 #7

    Doc Al

    User Avatar

    Staff: Mentor

    You can use Kepler's third law, or figure it out for yourself using what Astronuc posted. Either way, you'll get the same answer.
     
  9. Aug 4, 2005 #8
    I've been using Newton's third law all along, and its not working. I'll try again. What is it, just to make sure Im using the right formula???
     
  10. Aug 4, 2005 #9

    Doc Al

    User Avatar

    Staff: Mentor

  11. Aug 4, 2005 #10
    yeah, thats the one im using...wow I really dont think this problem is that hard. even tried it with period in minutes and seconds. oh well thanks anyways
     
  12. Aug 4, 2005 #11

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    The period should be in seconds, not minutes. And I agree with DocAl's question: a truck has a mass on the order of 10^4 kg. A planet would not be a planet unless it had a mass of at least 10^20 kg. Methinks there is a typo in your question.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Radius of orbit?
  1. Radius of Orbits (Replies: 36)

  2. Orbital Radius (Replies: 1)

  3. Orbital radius (Replies: 6)

  4. Radius of orbit (Replies: 7)

Loading...