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Homework Help: Velocity of a satellite in a eccentric orbit

  1. Dec 13, 2016 #1
    1. The problem statement, all variables and given/known data
    A satellite is orbiting an still planet, the farthest part of the orbit is at 200 km and the closest part at 100 km.

    what would be the speed of the satellite at the closest part of the orbit at 100 km if the speed at the farthest part is 1 m/s?

    2. Relevant equations

    3. The attempt at a solution
    I tried to apply conservation of momentum with which the result would be 0.5 m/s but im not sure if this result is valid for its posible the planet acquires a rotation to keep conservation of momentum true, value I dot know how to obtain.

    I was told to post this here though is not actually homework, Im already an engineer and finished already my studies but I still want to learn more
  2. jcsd
  3. Dec 13, 2016 #2


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    Staff: Mentor

    Are the given distances meant to be orbit radii or heights above the planet surface? It must be a very small planet if they are orbit radii!

    If they are heights above the surface then you will need additional information to establish either the true orbit radii (so, the radius of the planet) or the mass of the planet
    Conservation of angular momentum is a good approach, but as mentioned above you need a bit more information about the orbit to fix its size.
  4. Dec 13, 2016 #3
    As it gets closer the speed increases so 0.5 m/s cannot be th right answer in any case.
    But unless you specify what these distances mean, as suggested already, the only thing you can say is that the speed will be larger than 1 m/s.
  5. Dec 13, 2016 #4
    The distances are to the center of the planet, I suppose the planet has such a mass as to make the farthest orbit data posible

    My apologies im a bit dislexic i meant 2 m/s where i said 0.5 m/s

    Notice the radius halves which helps a lot in the calculations.
  6. Dec 13, 2016 #5


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    Science Advisor

    When the satellite is at 150 km from the planets center, what is the component of its velocity at right angles to a line drawn from the planet's center?
  7. Dec 13, 2016 #6
    thanks i found the solution to keep angular momentum true it would be 2 m/s
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