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Mechanical energy of a pendulum

  1. Jul 21, 2004 #1
    A pendulum of length 150cm swings with an amplitude of 1.8cm. Its mechanical energy is 6mJ. What is the mechanical energy of the same pendulum when it swings with an amplitude of 4.3cm? The answer is supposed to be in mJ.

    How do I relate the mechanical energy to what they gave me in the problem. I found the angular velocity, but did I need to do that? Is there an equation that relates energy with amplitude?

  2. jcsd
  3. Jul 21, 2004 #2

    Doc Al

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    Staff: Mentor

    Mechanical energy is kinetic energy plus potential energy. At the highest point in the pendulum's swing--when the height equals the amplitude--the energy is purely potential energy (presumeably measured from the bottom position).
    Yes, the formula for gravitational potential energy: PE = mgh
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