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Quick Gravitational Question

  1. Mar 28, 2013 #1
    Here is the question:

    Consider a pulsar, a collapsed star of extremely high density, with a mass M equal to that of the Sun (1.98 × 1030 kg), a radius R of only 12.7 km, and a rotational period T of 0.0545 s. By what percentage does the free-fall acceleration g differ from the gravitational acceleration ag at the equator of this spherical star?

    Just to make sure I am doing it right, I have the equations
    ag=GM/R^2
    g=ag-w2R

    and when I plug in the values I get ag=8.1881*1017
    g=8.18642*1011

    From what I gather from my textbook, ag is the gravitational acceleration and g is the free-fall.

    Now my predicament is that this is homework submitted online, I have a certain amount of submissions, and I only have one remaining.

    So when I compare the percentages, should I do ag/g*100=1.0002*108%
    or g/ag*100=.0001%

    Thanks
     
  2. jcsd
  3. Mar 28, 2013 #2

    jedishrfu

    Staff: Mentor

    your problem mentions differ so I think you need to calculate a difference ( (g - ag) / g) *100 but that's just my guess.
     
  4. Mar 28, 2013 #3
    that makes sense, but now I have to choose from ((g-ag)/g)*100=-1.0002e8 and
    ((ag-g)/ag)*100=99.9999

    but I guess since subtraction isn't reversible, it is most likely ((g-ag)/g)
     
  5. Mar 29, 2013 #4
    In the above problem accelaration increases so (ag-g)/g*100 is the correct answer
     
  6. Mar 29, 2013 #5
    "(ag-g)/g*100 is the correct answer"

    Indeed, thanks.
     
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