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Homework Help: NEED HELP natural pendulum

  1. Aug 9, 2008 #1
    The human leg can be compared to a physical pendulum, with a "natural" swinging period at which walking is easiest. Consider the leg as two rods joined rigidly together at the knee; the axis for the leg is the hip joint. The length of each rod is about the same, 54 cm. The upper rod has a mass of 7.0 kg and the lower rod has a mass of 4.3 kg.

    Calculate the natural swinging period of the system.
    Express your answer using two significant figures.

    I really need help..i am totally lost and it;s due in 3 hours...
  2. jcsd
  3. Aug 9, 2008 #2
    Show some effort first!

    I haven't seen this two pendulum system before but you must show your work before anyone else would help you (see rules).

    I can say assume it as one rod and find center of mass
    using the pendulum equations (that mgl = something .. I don't have my book near me for reference and I cannot remember those standard equations correctly) find T. (but this is just a guess)
    Last edited: Aug 9, 2008
  4. Aug 9, 2008 #3
    The lower leg will move about the knee at the endpoints of the swings and for one of the 2 swings in particular. Since there is no air resistance, you may avoid working with that; what you might want to take into account towards are fluctuations in the moment of inertia and see if there is any effect on the overall rotation.
  5. Aug 10, 2008 #4
    T = 2pi Squareroot (I//mgh)

    how do you determine moment of inertia, and h..

    For m do i use 7.0 kg or 4.3 kg
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