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Homework Help: Please Help Me

  1. Feb 11, 2007 #1
    Forces & Fields

    (a) calculate the gravatational potential pf a point A on the surface of the Earth
    (b) what is the gravatational potential of a point B, 1000km above A?
    (c) How much energy is expended if an object of mass 10kg were to just reach point B from A?

    I know the eq. for gravatational potential energy is U=-GMm/r ....but what do i use as my 2nd mass ??? :confused: please help im really lost :frown:
  2. jcsd
  3. Feb 11, 2007 #2


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    Staff Emeritus
    Science Advisor

    There is a difference between gravitational potential and gravitational potential energy.

    Gravitational potential is the potential energy per unit mass of an object due to its position in a gravitational field. The gravitational potential due to a point mass:

    Eg = -GM/r, where M is the mass of the object responsible for the gravitational field, whereas

    gravitational potential energy is given by

    mEg = -GMm/r

    Please refer to this page - http://hyperphysics.phy-astr.gsu.edu/hbase/gpot.html

    and the following plates including - http://hyperphysics.phy-astr.gsu.edu/hbase/gpot.html#gpi .
    Last edited: Feb 11, 2007
  4. Feb 11, 2007 #3
    Are my calculations correct? just want to make sure>
    a) -6.67*10^11 * 5.98*10^24/6.37*10^6 = -6.26*10^29

    b)-6.67*10^11 * 5.98*10^24/ 6.37*10^6+1000*10^3 = -5.41*10^29

    C)-6.67*10^11*5.98*10^24*10/6.37*10^6+1000*10^3 = -5.41*10^30
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