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Gravitation problem!

  1. May 18, 2010 #1
    1. The problem statement, all variables and given/known data
    At what height will the acceleration due to gravity will fall to 25% that of the earth's surface?



    2. Relevant equations
    g= GM/R^2


    3. The attempt at a solution
     
  2. jcsd
  3. May 18, 2010 #2

    rock.freak667

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    Homework Helper

    Good.

    You're missing this.
     
  4. May 18, 2010 #3
    g=GM/R^2 or R^2=GM/g..
    let g' be new value of g which is fall in 25%..
    therefore 25g/100= g' or g'=g/4

    R' be the new distance from surface of earth than,

    R'^2=GM/g'

    as g'=g/4 therefore

    R'^2=4GM/g

    as GM/g= R^2 therefore R'^2=4R^2

    R'^2= (2R)^2

    R' = 2R


    therefore answer is 'R' above surface of earth. As 2R is distance from center
     
    Last edited: May 18, 2010
  5. May 18, 2010 #4

    rock.freak667

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    Since they asked for the 'height' I would assume they want from the surface and not the distance from the center.

    But your method is correct.
     
  6. May 18, 2010 #5
    The answer given in my textbook is R. And I have worked it out with my friend and now I got the answer. But thanks to both of you for helping me solve this problem.
     
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