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Homework Help: Pendulum Difficulties.

  1. Jun 7, 2007 #1
    1. The problem statement, all variables and given/known data

    I have a lot of questions, but once I understand this I will get the basis for the other problems:
    Calculate the maximum speed of the 100g pendulum mass when it has a length of 100 cm and an amplitude of 50cm.

    2. Relevant equations

    3. The attempt at a solution

    ? nothing seems of usefulness, i dont know the questions i should ask myself
  2. jcsd
  3. Jun 7, 2007 #2
    Draw the pendulum at its highest point (amplitude of 50cm). What forces act on the ball at this point?

    Use the conservation of energy and a bit of trig.
  4. Jun 7, 2007 #3
    is there any way i can use the pythagorean theorem to solve this?
    Last edited: Jun 7, 2007
  5. Jun 7, 2007 #4
    can the pythagorean theorem be used for this?
  6. Jun 7, 2007 #5
  7. Jun 7, 2007 #6
    potential energy @ the top == kinetic energy @ the bottom

    You dun need Pythagorean theorem.
  8. Jun 7, 2007 #7
    i know i dont need it, but can it be done?
  9. Jun 7, 2007 #8
    no, it cannot be used.

    do you know about these formulas:
    U = mgh
    K = 0.5mv^2

    You need to use those two.
  10. Jun 7, 2007 #9
    no i dont know tose. argh im frustered
  11. Jun 7, 2007 #10
    what is u and what is k
  12. Jun 7, 2007 #11
    I think my main problem is not knowing what the height is!!!!!! b/c it doesn't seem like an amplitude on a pendulum can be the height, it seems more like the distance away from center.?
  13. Jun 7, 2007 #12
    is the answer 0.98 m/s ?? please help our i will never get to bed, just tell me if thats wrong. merci.
  14. Jun 7, 2007 #13
    You should know those formulas before touching this question.
    So, it might be good if you read a little about conservation of energy.
    For sure, that would help.

    I am assuming that you have a book, if you dunn, just reply and I will provide a link for that.
  15. Jun 7, 2007 #14
    "can the pythagorean theorem be used for this?"

    somehow yes

    you know the hypthenuse (length)
    you know the angle or angular amplitude of the motion (from the ampltude)
    (I assume the 'amplitude' is [angle in radians]*[radius of the circle])
    therefore you calculate the vertical displacement (make a drawing)
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