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Sattelite orbiting mars, work done to change distance.

  1. Dec 13, 2009 #1
    1. The problem statement, all variables and given/known data
    A 2700 kg spacecraft is in a circular orbit 1000 km above the surface of Mars. How much work must the spacecraft engines perform to move the spacecraft to a circular orbit that is 4000 km above the surface?

    mars: Mass=6.4185*10^23 KG, radius=3397000 m
    2. Relevant equations
    TME=U+KE
    U=Gm1m2/R
    KE=.5Gm1m2/r (this doesn't seem right for some reason)

    3. The attempt at a solution
    U1+k1+work=U2+k2
    work=U2+k2-(u1+k1)
    u1=2.630*10^10
    ke1=1.315*10^10
    U2=2.891*10^10
    Ke2=1.446*10^10
    TME1=3.945*10^10
    TME2=4.337*10^10
    Work= TME2-TME1=3.92*10^9
    webassign says I'm wrong. Is my equation for either KE or potential energy incorrrect? Any help is appreciated.
     
  2. jcsd
  3. Dec 13, 2009 #2
    Are you using a negative for U ?
     
  4. Dec 13, 2009 #3
    sure am
     
  5. Dec 14, 2009 #4
    Sorry for replying late, I have a final for this intro mechanics tomorrow morning :)
    This is the way i did it :

    E1 (energy at lower orbit) = -GmM/2r1 where r1 is the radius of mars + 1000 km
    E2 (energy at higher orbit)= -GmM/2r2 , r2 is the radius or mars + 1000 km

    m is 2700 kg
    M is mass of Mars.

    E2-E1 = GmM/2 (1/r1 - 1/r2) gives 5.33 x 10^9 J
     
  6. Dec 15, 2009 #5
    Thanks Ahmadmz, that's what I got too after I corrected my excel spreadsheet, had the wrong equation in for velocity. ( I do all my hw in excel)
     
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