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Gravitational force

  1. Mar 26, 2007 #1
    1. The problem statement, all variables and given/known data

    [​IMG]

    I just need help with part 3, if anyone can help me, i don't really know what to do

    2. Relevant equations
    F=k(q1)(q2)/r^2

    3. The attempt at a solution
     
  2. jcsd
  3. Mar 26, 2007 #2
    It is simple Newtonian Gravitation.
    F=G(mp)^2/r^2

    mp=mass of a proton
    G=Universal graviational constant
    mp is squared because it is two protons, otherwise it would be m1 and m2
     
  4. Mar 26, 2007 #3
    G is constant, but i am unsure of how to get mp
     
  5. Mar 26, 2007 #4
    The mass of a proton is constant. It should be locatable in any physics book or going to google and typing mass of a proton
     
  6. Mar 26, 2007 #5
    Okay, i got: 16726E-27^2 * G / .0071^2
    = 3.6627E-52
     
    Last edited: Mar 26, 2007
  7. Mar 26, 2007 #6
    i submitted it but got it wrong, but i have a few more tries to get it right, what did i do wrong?
     
  8. Mar 26, 2007 #7

    hage567

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    That’s 1.6726x10^-27 kg for the mass of a proton, right? It looks like you were missing the decimal in there.
     
  9. Mar 26, 2007 #8
    now i got 3.66e-60
     
  10. Mar 26, 2007 #9

    hage567

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    Did it work? It should.
     
  11. Mar 26, 2007 #10
    it says it is wrong, not sure why though, i double checked. it seems like it should be right
     
    Last edited: Mar 26, 2007
  12. Mar 26, 2007 #11

    hage567

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    Well, I get 3.70x10^-60 N, so maybe it is a rounding issue? I don't know how picky web programs are about that kind of thing. I can't see why the answer would be wrong.
     
  13. Mar 26, 2007 #12
    i have 1 guess left, i will try 3.70x10^-60 N
     
  14. Mar 26, 2007 #13
    hmm maybe not, one of my previous guesses was 3.69e-60, that probably should have been correct
     
  15. Mar 26, 2007 #14

    hage567

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    Sorry, I just am not able to see what could be wrong with that calculation.
     
  16. Mar 26, 2007 #15
    thank you for all of your help
     
    Last edited: Mar 26, 2007
  17. Mar 26, 2007 #16
    i got it incorrect, but the answer was 3.811e-60
    have no idea how they got that, ill have to check with my teacher because i still think the other answer is correct, maybe it is a mistake
     
  18. Mar 26, 2007 #17

    hage567

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    A different value for the proton mass was probably used. If I work it out backwards I get 1.697x10^-27 kg for the mass. Not the right one as far as I'm concerned.
     
  19. Mar 26, 2007 #18
    i think i will ask my teacher, maybe she will give it to me
    thank you very much for all of the help!
     
  20. Mar 26, 2007 #19
    It may be, just may be, that the program assumes the value of the proton mass to be 1.67e-27 - just to two decimal places.
     
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