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: Satellite in an orbit around Eart

  1. Dec 6, 2006 #1
    1. The problem statement, all variables and given/known data
    A satellite in an orbit around Earth has velocities between Vmin=V-V0 and Vmax=V+V0. Find the eccentricity of the orbit.

    2. Relevant equations
    rmin=l^2/(Gm1m2*mu*(1+e))
    E=(Gm1m2)^2*mu*(e^2-1)/2l^2
    where mu = reduced mass = m1m2/m1+m2

    3. The attempt at a solution
    I know all this formulas for eccentricity, but they all involve disctances/or energy, but not velocities! I don't even know how to start solving this.... Any help/hints?

    Thank you very much in advance!
     
  2. jcsd
  3. Dec 6, 2006 #2

    nrqed

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member


    You may use conservation of angular momentum to relate the speed at aphelion to the speed at perihelion. Recall, [itex] {\vec L} = {\vec r} \times {\vec p} [/itex]. Since at aphelion and at perihelion the motion is perpendicular to the position vector, you get that [itex] r_{min} v_{max} = r_{max} v_{min} [/itex]. Since [itex] r_{min} = a(1-e) [/itex] (*if* I recall correctly) and [itex] r_{max} = a(1+e) [/itex] , you get a simple equation relating the max and minimum speeds. You will get a simple expression for the eccentricity in terms of V and V_0.

    Hope this helps.

    Patrick
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook