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Homework Help: Pendulum Problem

  1. Dec 12, 2011 #1
    The problem statement, all variables and given/known data[/b]
    An actor of mass 65.0 kg wishes to make a grand entrance onto a stage during a play. He attaches himself to a cable having length R=5.00 m. A stagehand gives the actor a push, imparting an initial speed onto the actor at heigh 1.5 m above the lowpoint of his ensuing motion. As the actor swings through the lowest point of his motion, his speed is 6 m/s. Length R remains Constant. What is the initial speed of the actor?

    The attempt at a solution[/b]
    I think I have literally tried everything. I attempted to find theta between the two points and, if done correctly, got that to be 25.8 degrees. I then tried finding arc length, which came out to a crazy number. Then I tried using angular acceleration equations. THEN I tried calculating it using K+U(initial)=K+U(final), but I ran into troubles there when it came to "y".
  2. jcsd
  3. Dec 12, 2011 #2
    Look at the problem from an energy conservation standpoint. You have an unknown initial KE. You have a known final KE. You can determine the change in PE.
  4. Dec 12, 2011 #3
    You can tackle this by considering PE and KE. When the actor is pushed he is given some KE and he also has some PE relative to the lowest point (1.5m) of his swing
    KE = 0.5mv^2 PE = mgh
    At the lowest point he has KE
    The details about the pendulum seem to be irrelevant unless you have been asked something else
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