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Pendulum problem-last answer was wrongneed help please

  1. Mar 2, 2008 #1
    pendulum problem--last answer was wrong..need help please!!

    A small rock with mass 0.12 is fastened to a massless string with length 0.80 to form a pendulum. The pendulum is swinging so as to make a maximum angle of 45 with the vertical. Air resistance is negligible.

    What is the speed of the rock when the string passes through the vertical position?

    What is the tension in the string when it makes an angle of with the vertical?

    What is the tension in the string as it passes through the vertical?
     
  2. jcsd
  3. Mar 2, 2008 #2
    For the first question you need to look at conservation of energy. The pendulum is at its lowest point when in the vertical position, so it has no potential energy. Thus all energy must be kinetic. Likewise, when its at the highest position (454 degree angle with vertical), it has no kinetic energy but maximum potential energy.
     
  4. Mar 2, 2008 #3
    thanks!! i figured it out a little bit ago though!
     
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