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!

Orbiting satellite

  1. Jun 28, 2005 #1
    When in orbit, a communication satellite attracts the earth with a force of 16.7 kN and the earth-satellite gravitational potential energy (relative to zero at infinite separation) is - 1.43*10^11 J. Find the satellite's altitude above the earth's surface. The radius of the earth is 6.38*10^6.

    OK, I must be making this harder than it needs to be. What I've been trying to do is to use the formulas for gravitational force to get an equation with two unknow variables (Mass of the satellite and height above earth's surface) And I do the same for gravitational potential energy. Then, since both equations have the same two unknown variables, I solve for one of them and substitute. Is there another way of doing this? Am I doing it copmletely wrong? Please help me!!! :confused:
     
  2. jcsd
  3. Jun 28, 2005 #2
    You sound like you have the right idea. Give it a shot.
     
  4. Jun 29, 2005 #3
    Total Energy of a satellite revolving around earth is given by:

    [itex]- \frac{GMm}{2r}[/itex]

    BJ


    Note:This post has been edited after Older Dan's remarks.
     
    Last edited: Jun 29, 2005
  5. Jun 29, 2005 #4

    OlderDan

    User Avatar
    Science Advisor
    Homework Helper

    There is no 2 in the potential energy. Perhaps you meant the total energy

    [itex] U = - \frac{GMm}{r} [/itex]

    [itex] T = \frac{1}{2}mv^2 = \frac{r}{2} \left( \frac{mv^2}{r} \right) = \frac{r}{2} \left| F_c \right| = \frac{r}{2} \left( \frac{GMm}{r^2} \right) = \frac{GMm}{2r} = -\frac{1}{2} U [/itex]

    [itex] E\ \ =\ \ T\ \ +\ \ U = \frac{GMm}{2r}\ \ -\ \ \frac{GMm}{r}\ \ =\ \ - \frac{GMm}{2r} [/itex]
     
  6. Jun 29, 2005 #5
    You are doing the right thing ninjagowoowoo, you should be able to find both the mass and height of the satellite with this method. In fact, this question was answered on this forum a long time ago (well it's in the archive)

    https://www.physicsforums.com/archive/t-69703_Gravitational_forces.html

    Hope that helps!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Orbiting satellite
  1. Satellite Orbits (Replies: 6)

  2. Satellite Orbit (Replies: 5)

  3. Satellites in Orbite (Replies: 9)

  4. Satellite in Orbit (Replies: 6)

  5. Satellite orbit (Replies: 12)

Loading...