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Homework Help: Kinetic energy problem

  1. Nov 13, 2011 #1
    1. The problem statement, all variables and given/known data
    How much energy is required to move this satellite to a circular orbit with a radius of 2.50×104 miles?

    I've found the answer to Part A of this problem to be 1.59*10^10, if this helps solve the above^^
    (Find the kinetic energy of a 1.80×103 kg satellite in a circular orbit about the Earth, given that the radius of the orbit is 1.40×104 miles.)

    2. Relevant equations
    v^2=G Me / r
    KE = 1/2mv^2
    .5*m*v^2=.5*m*(G*mEarth/R)
    E = 1/2mv^2 - GMm/r
    KE = 1/2mv^2 = 1/2 GMm/r

    E = -1/2 GMm/r
    dE = E2 - E1 = GMm*(-1/r2 +1/r) = GMm*(r2 -r)/(r*r2)

    3. The attempt at a solution
    using these formulas have given me three wrong attempts on my homework and i don't know what i'm doing wrong. any help would be very appreciative.
     
  2. jcsd
  3. Nov 14, 2011 #2

    BruceW

    User Avatar
    Homework Helper

    It all looks fine, except, on you final equation, you forgot the 1/2. So it should be:
    dE = 0.5 GMm*(r2 - r)/(r*r2)
    If you're still getting it wrong after changing this, then maybe you've not converted from miles to meters properly?
     
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