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: Find angular momentum of a body moving around other in elliptical path?

  1. Mar 2, 2012 #1
    planet of mass m is moving in an elliptical orbit around the sun of mass M. maximum and minimum distance of the planet from the sun is r1 and r2. Find the angular momentum of planet about the sun.(Consider M to be fixed in it's position.)

    Angular momentum= m(R*v)
    At farthest point from sun angular momentum is mr2v2
    and at the closest point it is mr1v1
    I am thinking to make third equation with the forces of interaction between the two bodies bodies. that might be something like centrifugal force = gravitational force of interaction, but i don't know that value of instantaneous radius of curvature of the m at the two points.

    So this is my problem. what should i do?
  2. jcsd
  3. Mar 2, 2012 #2


    User Avatar

    Staff: Mentor

    What information about the orbital parameters can you extrapolate from the perihelion and aphelion distances?

    To find the angular momentum it seems that it'd be handy to know the velocity at either perihelion or aphelion. Sounds like kinetic and potential energy will play a role...
  4. Mar 2, 2012 #3
    thanks! . these words are enough to hint me. (why didn't it strike in my mind)

    r1 is the closest point on the major axis of elliptical path of planet(idk is it perihelion or aphelion). and the farthest distance that also lies on major axis is r2

    OK!. thanks for replying. I have got the answer....
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook