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Homework Help: Simple problem of gravitational field

  1. Aug 19, 2009 #1
    1. The problem statement, all variables and given/known data

    What is the magnitude of the gravitational field at the surface of a neutron star whose mass is 1.80 times the mass of the Sun and whose radius is 9.3 km?

    2. Relevant equations

    g = GM/r2

    3. The attempt at a solution

    G is ofcourse 6.67x10^-11
    r^2 is 8.649x10^7 m

    Now I don't know what to take as mass. I took just 1.8 and it didn't work. I just took the mass of sun as 1.9x10^30kg and it didn't work and I also tried the product of those two.
    What am I missing?
    Okay I tried all I could but I am now stuck. Can someone help me. Thanks so much.
  2. jcsd
  3. Aug 19, 2009 #2
    It appears you have everything you need. If the nuetrons star's mass is 1.8 times the suns, you should just times the suns mass by 1.8, which it appears you've done.
    I would just check everything is in SI units and maybe reread the question.
  4. Aug 20, 2009 #3
    Thanks, I double checked everything yet nothing seems to work.
    Even tried a negative sign in front of all possible answers.
  5. Aug 20, 2009 #4
    Apparently the STUPID hw system does not recognize x 10^y format yet the only error it gives is incorrect answer.
  6. Aug 20, 2009 #5
    if you don't mind, can you tell me what you've been getting as the answer? Maybe i can check if its just a computational error
    also, it sounds like its a multiple choice qu, so maybe you should check their units too? Not really sure what the problem is.
  7. Aug 20, 2009 #6

    We have an online system where you input the answer and it says if it's correct or not. If it's correct you get the points.
    2748510000000 m/s^2 is the answer and the system recognized it (ie it's correct)
    I was inputting the number as 2.748 x 10^12 and hence the system said incorrect answer which is poor design of the system IMHO

    And it's not multiple choice
  8. Aug 20, 2009 #7
    hmm, i got a similar answer, but i used a different measurement for the sun's mass (through google). I've never used the system you've described, but it might help to try looking up the sun's mass to a greater accuracy. Even if you were to round it, it looks closer to 2x10^30 than 1.9. Other than that, i'm not sure what else there is besides fiddling with the numbers
    I'd help you more, but I gotta get some sleep, its like 2 in NY. good luck with that system though.
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