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Homework Help: Difference in Planet Mass

  1. Oct 4, 2005 #1
    I think I have done this problem correctly,

    The mass of a robot is 6680 kg. This robot weighs 3070 N more on planet A than it does on planet B. Both planets have the same radius of 4.00 x 10^8. What is the difference Ma - Mb in the masses of these plantes?

    I used this equation F = G * (m1*m2)/(r^2)
    F = 3070 N
    m1 = robot
    mb = extra mass of planet A
    r = 4.00 x 10^8

    3070 = 9.673 x 10^-11 * 6680m2/ (4.00 x 10^8)^2
    3070 = (2.786 x 10^-24)m
    1.1019 x 10^27 = m

    Is this correct or do I have it totally wrong?

  2. jcsd
  3. Oct 4, 2005 #2


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    Homework Helper

    I got a different answer, you seem to have typed it wrong into your calculator, the equation's the same as mine.

    EDIT: Never mind. I had used the gravitational constant you typed, which was wrong :). I got the same answer now.
    Last edited: Oct 4, 2005
  4. Oct 4, 2005 #3
    I tried it, though not using your technique, and your answer seems correct. Same answer from two different methods is usually a good sign.
  5. Oct 4, 2005 #4
    Although your answer should be in kg, not m.
  6. Oct 4, 2005 #5

    I just wanted to make sure before I typed it into GradePlus. It was correct (I had already used up a try as I couldn't get the entire number in, but found out I could use Exponents) I asked my Physic teacher if I did the problem correctly and he started to do the problem, and he couldn't do the problem.

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