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Homework Help: The Earth and the Moon

  1. Jan 31, 2009 #1
    1. The problem statement, all variables and given/known data

    Supppose that electrical attraction, rather than gravity were responsible for holding the moon in orbit around the earth. If equal and opposite charges Q were placed on the earth and the Moon, What should be the value of Q to maintain the present orbit?

    Treat the Earth and Moon as point particles

    2. Relevant equations

    Mass of earth: 5.97x1024kg
    Mass of moon: 7.35x1022kg
    radius of orbit: 3.84x108m

    Fg=Gm1m2 / d2
    Fe= kq1q2 / d2

    3. The attempt at a solution

    Well I know to start by finding the force of gravity, but from there i am unsure about how to do this problem. Could someone please help?
  2. jcsd
  3. Jan 31, 2009 #2
    If the orbit remains the same, then so does the acceleration.
    Since the masses are the same, so are the forces: Fg=Fq
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