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Homework Help: Can someone Check this (Energy Question)

  1. Nov 24, 2006 #1
    Q: Calculate the total engery of a geosynchonous satellite (one that orbits over a fixed spot) with amass of 1500 kg, orbiting earth at height 325 km (325 000m) with an orbital speed of 5000 m/s or 5.0x10^3

    My Solution: Et = Ep + Ek
    Ep = Mg delta H
    Ek = 1/2 (m) V^2
    thus Et = Mg(H) + 1/2 (m) v^2
    (1500)(9.8)(325000) + 1/2(1500) (5000)^2
    = 4.78x10^9 + 1.875x10^10
    =2.353x10^10 j or 2.353x10^7 Kj

    Is there a mistake in my calculations or has this question been done correctly?
     
  2. jcsd
  3. Nov 24, 2006 #2

    PhanthomJay

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    using g = 9.8m/s/s is valid only near earth. What can you say about GPE at those heights?
     
  4. Nov 24, 2006 #3
    i have no idea? is it 0? or is it very small? i have no idea
     
  5. Nov 24, 2006 #4

    Doc Al

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    Look up the general expression for the gravitational PE between two masses (such as the earth and a satellite).

    As PhanthomJay pointed out, mgh is only useful for finding changes in PE for objects close to the surface of the earth.
     
  6. Dec 5, 2006 #5
    ok.. Ep = Gm1m2/r
     
  7. Dec 5, 2006 #6

    Doc Al

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    Don't forget the minus sign: Ep = -Gm1m2/r
     
  8. Dec 5, 2006 #7
    ok thank you
     
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