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Homework Help: Gravitational Field Strength Help

  1. Oct 4, 2008 #1
    Hello Everyone, I've been trying to get the answer to this problem for ages now and I just can't match my answer with the one in the back of the textbook. I hope you can let me know what I'm doing wrong.

    1. The problem statement, all variables and given/known data
    What is the gravitational field strength at a place 220 km above Earth's surface, the altitude of many piloted space flights.

    2. Relevant equations
    Fg = mg
    Fg = Gm₁m₂/d²

    3. The attempt at a solution
    d = 6.60 x 10³ km
    G = 6.67 x 10-¹¹ N.m²/kg²
    m₂ = 5.98 x 10²⁴ kg
    g = ? N/kg

    Fg = mg = Gm₁m₂/d²
    mg/m = Gm₁m₂/d²/m
    g = Gm₂/d²
    g = (6.67 x 10-¹¹ N.m²/kg²)(5.98 x 10²⁴ kg)/((6.60 x 10³ km)²)

    And when I do this I always get the wrong answer when I compare it with the one in the back of the textbook. The answer in the back of the textbook is 9.1 N/kg [down].

    If anyone here could please help me with this, that would be great.

  2. jcsd
  3. Oct 4, 2008 #2
    Equation looks fine to me, I solved it and got 9.18 N/kg
    what did you get?
  4. Oct 4, 2008 #3
    Thanks, I guess I was doing it right, I just forgot to convert the distance in to meters.
  5. Oct 4, 2008 #4
    oh of course, how could I overlook that. I didn't follow your equation, I did it myself. I should have checked your equation more thoroughly!
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