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Homework Help: Gravitational Force (Earth and Sun)

  1. Jan 24, 2008 #1


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    Gold Member

    1. The problem statement, all variables and given/known data

    To better comprehend the gravitational force between the Earth and the Sun, pretend gravity is turned off and the pull replaced by the tension in a steel cable joining them. How thick would such a cable need to be? You can estimate the diameter by knowing the tensile strength of steel cable is about 5.1 * 10^8 N/m^2.

    2. Relevant equations

    Any equations concerning gravitation/cirular motion.

    3. The attempt at a solution

    This is my attempt at a solution, the answer key says it's wrong.

    F = m(4)(pi^2)(r)/t^2

    d^2 = m(4)(pi^2)(r)/(t^2)(tensile strength)

    thickness = m(4)(pi^2)/(t^2)(tensile strength)

    thinkness = 465.45 m or 0.465 km

    Where have I gone wrong in my calculations? Can someone please steer me in the right direction. Thanks.
  2. jcsd
  3. Jan 25, 2008 #2

    Shooting Star

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    Homework Helper


    Didn't understand.

    Try to think simply.

    Max tensional force/cross-sectional area of cable = tensile strength =>
    Centripetal force/area = tensile strength.
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