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Homework Help: Gravitational Pulls- Acceleration decreases as object is farther from center

  1. Oct 15, 2008 #1
    1. The problem statement, all variables and given/known data

    A sensitive gravimeter at a mountain observatory finds that the acceleration due to gravity is 0.0057 m/s2 less than that at sea level. What is the observatory's altitude?

    2. Relevant equations

    g= (GM)/r^2

    3. The attempt at a solution

    Alrighty, my attempt makes sense to me, so I'm sure where I'm going wrong.

    I began by finding the mass. So, I used 9.8 m/s2 as the g and then the earth's radius as r:

    9.8= (6.67E-11)M/6.37E6 (<----- the earth's radius)

    M= 9.359E17 kg

    Then I subtracted the acceleration change given from 9.8:

    9.8-0.0057 = 9.7943 m/s2
    That is my new g.

    Then, using the found mass, I plugged in my new numbers:

    9.7943= (6.67E-11)(9.36E17)/ r^2
    r=2523.4 m

    That, however, was not the correct answer. I can't see my error. Could anyone help me out?

    Thanks in advance!!

  2. jcsd
  3. Oct 16, 2008 #2


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    Science Advisor

    Do you need to square the earth's radius?
  4. Oct 16, 2008 #3
    Sorry. I never came back to edit that out. My mistake. I actually realized that I was being dense and could just use the earth's mass- 5.98E24.

    Yet this is still the incorrect answer. Can anyone help me?
  5. Oct 16, 2008 #4

    D H

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    Staff Emeritus
    Science Advisor

    We can't tell why your result is incorrect if you don't tell us what your result is and how you obtained it. In other words, show your work, please!
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