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Moon gravity problem

  1. Aug 2, 2004 #1
    (6.67 x 10 ^-11 N m^2/kg^2) (7.36 x 10^22 kg)
    (1.74 x 10^6m) ^2


    6.67 x 7.36
    ___________ x 10^-11=22-6(2) x Nm^2/kg^2 * kg
    1.74 ^2 ____________ _____________
    (10^6)^2 m^2

    16.2 x 1 x 10 ^-13 n/kg

    What am I doing wrong??
  2. jcsd
  3. Aug 2, 2004 #2


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    Have a look at what you wrote, it's impossible to read. Moreover, I have no idea what you're doing, and why. What is the actual question you're trying to answer? Is this simply an error in your computation? If so, I suggest you use a calculator.
  4. Aug 2, 2004 #3
    This problem was given on a previous test...the problem is written exactly as seen on the actual exam:

    Moons gravity is (6.67 x 10 ^-11 N m^2/kg^2) (7.36 x 10^22 kg)
    (1.74 x 10^6m) ^2

    I was to simplify and give units....I ended up w/ an incorrect answer and I did all the steps...
  5. Aug 2, 2004 #4


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    1.62 N/kg

    Look at the dimensions, you'll see that it ends up being N/kg. Use a calculator, and you'll get a number like:


    Only keep 3 significant digits and you'll get what I got. Were you allowed to use a calculator? If so, I don't see what was so hard. If not, the question is ridiculous.
  6. Aug 2, 2004 #5

    matt grime

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    I think we're supposed to comment on:

    [tex] \frac{(6.67 * 10^{-11})*(7.36*10^{22})}{(1.74*10^{6})^2}[/tex]

    and its simplification to, hopefully, whatever the result of (6.67*7.36)/(1.74)^2 is times 10^{-1}
    you appear to have used the 10^{6} in the denominator twice.
    note you can't assume that what you type in the white box will come out the same in the finished article; fixed width fonts anyone? plus all spaces are treated equally, I think. click on the pretty tex to see how to do it
  7. Aug 2, 2004 #6

    Doc Al

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    You handled the exponents incorrectly:
    [itex]10^{-11} * 10^{22} / (10^6* 10^6) = 10^{(22-11)}/10^{12} = 10^{11}*10^{-12} = 10^{-1}[/itex].
  8. Aug 2, 2004 #7


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    Specifically, you started off good, then did too much of a good thing.

    You started off with 10^ [-11+22-6(2)], which is the right way to handle the exponents ( I think, assuming you meant + instead of =).

    Then you subtracted the exponents in the denominator again.
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