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Force on satellite from earth

  1. Nov 15, 2009 #1
    1. The problem statement, all variables and given/known data
    A communications satellite with a mass of 450 kg is in a circular orbit about the Earth. The radius of the orbit is 2.9×104 km as measured from the center of the Earth. A. Calculate the weight of the satellite on the surface of the Earth. B. Calculate the gravitational force exerted on the satellite by the Earth when it is in orbit.


    2. Relevant equations
    Weight=mass*gravity


    3. The attempt at a solaution
    I found A. 4400 N
    I dont know how to try to find B.
     
  2. jcsd
  3. Nov 15, 2009 #2

    ideasrule

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    Homework Helper

    What's the formula for gravitational force?
     
  4. Nov 15, 2009 #3
    for B) use newtons universal law of gravity.

    namely:

    [tex]F=\frac{GMm}{r^2}[/tex]

    G= newtons gravity constant
    M= mass of earth
    m= mass of satellite
    r= radius of orbit

    note:(both newtons constant & the mass of earth can be found on the internet)
     
  5. Nov 15, 2009 #4
    sorry ideasrule, i gave it away :blushing:
     
  6. Nov 15, 2009 #5
    i tried that but it was wrong
    F=((6.67E-11)(5.97E24)(450))/(2.9E4)^2=213067241.4 this isnt right, what am i doing wrong
    G=6.67E-11
    mass od earth= 5.97E24
     
  7. Nov 15, 2009 #6
    you must convert your radius from Km to m. Always double check your units...

    (it cost NASA millions one time)
     
  8. Nov 15, 2009 #7
    alright, i got it, thanks
     
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