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Homework Help: Maximum kinetic energy of a pendulum

  1. Jul 3, 2011 #1
    1. The problem statement, all variables and given/known data
    Okay, so I'm using the online Giancoli physics thing for AP Physics C summer work (see: "([PLAIN]http://wps.prenhall.com/esm_giancoli_physicsppa_6"[/URL]. [Broken] I think my way of doing it is correct, but the online checker says I'm wrong.
    The question: "A pendulum has a mass of 3.2 kg, a length of 1.5 meters, and swings through a (half)arc of 17 degrees. To the nearest tenth of a Joule, what is its maximum kinetic energy of the pendulum?"

    2. Relevant equations
    PE = mgh
    KE = 1/2mv^2

    3. The attempt at a solution
    Find the PE of the pendulum. The height of it at 17 degrees: .43856 meters (about).
    PE = 3.2*9.81*.43856 = 13.767 Joules. But the online checker says 2.1 Joules.

    What am I doing wrong? Or, am I doing it right, the online thing is just wrong?



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    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jul 3, 2011 #2


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    Staff: Mentor

    Your height for the pendulum bob is not correct.
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