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Homework Help: Force of gravity problem

  1. Mar 23, 2015 #1
    1. The problem statement, all variables and given/known data
    A 12 kg meteor experiences an acceleration of 7.2 m/s2, when falling towards the Earth.

    A) How high above the Earths’ surface is the meteor?

    B) What force will a 30 kg meteor experience at the same altitude?

    Starting to get more comfortable with my calculations. If there are any blunders or things I could have done to make my work more clear, any suggestions would be appreciated.

    2. Relevant equations
    r = √ G m / g

    3. The attempt at a solution

    r = √ G m / g

    r = (6.67 x 10-11) (5.98 x 1024) / 7.2 = 7.4 x 106

    7.4 x 106 - 6.38 x 106 = 1060

    r = 1060 km


    Mass is irrelevant
  2. jcsd
  3. Mar 23, 2015 #2

    Simon Bridge

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    Well done - I had a slight hesitation there thinking it may be a terminal velocity problem but the distance is too great for that and the context all wrong.

    A. finesse the long-answers by writing a sentence stating the result:
    "the meteor is 1060km above the Earth's surface".

    B. Mass is relevant - the acceleration of gravity does not depend on the mass but the question asks for force.
  4. Mar 23, 2015 #3


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    Right answer, but I would have calculated it using ratio to 9.8m/s2: ##(R+x)^2g_{R+x}=R^2g_R##
    Read the question more carefully.
  5. Mar 24, 2015 #4
    Wow, completely misread the question. How embarrassing..

    Then F = m a,
    F = (30) (7.2)
    F = 216 N [toward Earth]
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