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Earth's gravitational field strength

  1. Sep 26, 2008 #1
    1. The problem statement, all variables and given/known data
    (a) Find the altitude above the Earth's surface where Earth's gravitational field strength would be two-thirds of its value at the surface. Assume re = 6.371 multiplied by 10^3 km.
    wrong check mark km
    (b) Find the altitude above the Earth's surface where Earth's gravitational field strength would be one-third of its value at the surface.
    wrong check mark km

    [Hint: First find the radius for each situation; then recall that the altitude is the distance from the surface to a point above the surface. Use proportional reasoning.]


    2. Relevant equations
    F = GMm/r^2


    3. The attempt at a solution
    I have tried it and I am either calculating wrong or setting it up wrong... or both. One problem I see with the formula is that it doesnt have the mass of the second object.. so I dont know what to do there.
     
    Last edited: Sep 26, 2008
  2. jcsd
  3. Sep 26, 2008 #2
    you do not need to know the mass of the second object. F=ma and the masses of the second object cancel out. a=9.8m/s^2 on earth and at the point above the earth a=9.8/3 let r=radius of earth + altitude. then plug in and solve for a.
     
  4. Sep 26, 2008 #3
    Sorry but that still isn't helping me. Are you just using the F=ma formula?
     
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