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Angular acceleration. Please help

  1. Mar 29, 2007 #1
    1. rotating door is made from four rectangular glass panes, as shown in the drawing. The mass of each pane is 95 kg. A person pushes on the outer edge of one pane with a force of F = 80 N that is directed perpendicular to the pane. Determine the magnitude of the door's angular acceleration.

    The with of each pane to the rotation axis is 1.2m

    This is how I approached it

    a= f/m =80/95 = 0.84

    Now Tangential Acceleration a = angular acceleration x radius

    angular acceleration = tangential acceleration/radius

    = 0.84/1.2 = 0.70 rad/m^2

    this answer was wrong

    3. The attempt at a solution
  2. jcsd
  3. Mar 29, 2007 #2


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    Since the movement is rotational, you should use torque and momentum of inertia, instead of force and mass.
  4. Apr 1, 2007 #3

    How do I do that? Where do i start? please hep
  5. Apr 1, 2007 #4


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    Staff Emeritus
    Science Advisor

    Well, what do you know about torque and moment of inertia? In particular, do you know how to relate torque to the angular acceleration?
  6. Apr 20, 2007 #5
    no. I don't
  7. May 7, 2007 #6


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    Staff Emeritus
    Science Advisor

    Well firstly you need to work out the moment of inertia of the door. Could you explain more precisely what the diagram looks like? Do you know what the moment of inertia is? Do you know how to find the moment of inertia of a solid object? Have you come across anything in your textbook relating it and the torque to the angular acceleration?

    As an aside, in response to your pm, I'm sorry-- I can't keep track of every thread I help in.
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