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Math Help - Gravity

  1. #1
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    Gravity

    When a satellite is a distance R from the center of Earth, the force due to gravity on the satellite is F. What is the force due to gravity on the satellite when its distance from the center of Earth is 3R?

    (1) F/9 (3) F
    (2) F/3 (4) 9F
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by symmetry View Post
    When a satellite is a distance R from the center of Earth, the force due to gravity on the satellite is F. What is the force due to gravity on the satellite when its distance from the center of Earth is 3R?

    (1) F/9 (3) F
    (2) F/3 (4) 9F
    You should know that at the level you are working gravity acts via
    an inverse square law. So:

    F(kx)/F(x)=1/k^2,

    In you case k=3, so F(3R)=F(R)/9.

    So the answer is (1).

    RonL
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  3. #3
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    ok

    Thanks! I did not know that formula.
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by symmetry View Post
    Thanks! I did not know that formula.
    The question obviously presupposes that you know that gravity acts
    via an inverse square law. The relation:

    F(kx)/F(x)=1/k^2,

    is an imeadiate consequence of the inverse square law.

    RonL
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