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Homework Help: Planet and speff problem find mass

  1. Nov 16, 2011 #1
    1. The problem statement, all variables and given/known data
    The weigh tof spaceman speff, soley due to the gravitational pull of planet x at its surface is 389N. If he moves to a distance of 1.86*10^4km above the planets surface his weight changes to 24.31N. What is the mass of planet xif speffs mass is 75 kg.

    2. Relevant equations


    3. The attempt at a solution
    i know the answers is 2.96*10^24 kg. nut idk how to get it
  2. jcsd
  3. Nov 16, 2011 #2


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    I would double check your second equation.
  4. Nov 16, 2011 #3
    it m1*m2
  5. Nov 16, 2011 #4
    what else?? im still not getting it
  6. Nov 17, 2011 #5


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    Use the F=G·m1·m2/r2 equation, and plug in the given information. There are two sets of information, so you would get two equations:

    (1) 389 N = G · __ · __ / __
    (2) Use the other weight given in the problem to set up the second equation
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