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Homework Help: Conservation of Energy Problem

  1. Dec 25, 2013 #1
    1. The problem statement, all variables and given/known data

    A 2 meter long pendulum passes its lowest point with a velocity of 4 m/s, then swings back up before temporarily coming to a stop. What angle does it then form with the vertical, if the air resistance is negligible?

    2. The attempt at a solution

    I know that the kinetic energy at the bottom will equal the potential energy at the top - that is when the pendulum comes to a temporary stop.

    KE = PE

    (1/2)(m)(16) = (m)(g)(h)

    h = 0.82 meters

    Now, I understand that this is the max height above the lowest point.

    I can't figure out how to proceed from here. I don't have two components to find the angle.
  2. jcsd
  3. Dec 25, 2013 #2
    Actually you do have two components, you have the height at the instance where it is coming to rest, and you have the radius of the pendulum.
  4. Dec 25, 2013 #3
    I don't quite follow.

    Attached Files:

    • Pcl.png
      File size:
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  5. Dec 25, 2013 #4


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    2017 Award

    Staff: Mentor

    The vertical, dashed line is the radius as well.
    What happens if you add a horizontal line at the height of your object?
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