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Homework Help: Simple pendulum problem

  1. Nov 22, 2007 #1
    1. The problem statement, all variables and given/known data

    A sphere of mass 0,5 kg bounces from 2 extreme positions like a pendulum. When it makes a 25º with vertical the sphere is 20 cm high from equilibrium position and the tension value is 5,5 N.


    - Total acceleration
    - Length of the wire
    - velocity modulus in that position
    - minimum value for the tension in the wire

    2. Relevant equations

    3. The attempt at a solution

    in the previous expressions v2 is v square and at is tangential acceleration

    I dont know how to find v or r (the lenght of the pendulum). Can you help? Thanks
  2. jcsd
  3. Nov 22, 2007 #2
    I think you could introduce: mgh = 1/2mv^2 to find v.
    And somehow you use 20cm to calculate h.
  4. Nov 22, 2007 #3
    i think that your suggestion only gives v if the pendulum has started its motion from an angle that corresponds to h=20 cm.
  5. Nov 22, 2007 #4
    Hello, friends!
    A great help would be if someone can say that this problem has a solution!
  6. Nov 22, 2007 #5

    Shooting Star

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    Homework Helper

    Drawing a diagram and dropping a perp on the vertical at the mean position from the bob when it's at 25 deg, r-20 = r*cos 25 gives you r, where r is the length of the pendulum. Now find v.
  7. Nov 22, 2007 #6
    Thanks very much to all :)
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