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Homework Help: A box on a board

  1. Jan 15, 2009 #1
    Let's say you put a box on a board, like this. (the dot represents a fulcrum point). Let's say the center of mass is exactly halfway between the fulcrum and the edge of the board.

    http://dl.getdropbox.com/u/119319/board.jpg [Broken]

    Now let's say you exert an upward force F in the direction of the arrow. My book tells me that the force should be reduced by a factor of 2.. which I suppose is plausible, but how can you know the exact mechanical advantage without knowing the length of the board?
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jan 15, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Can you figure out the mechanical advantage if you knew the length of the board? Call the length L and see what happens.
  4. Jan 15, 2009 #3
    Okay, I think I was confused because I didn't really understand the definition of a 'lever arm.' The lever arm is defined as the distance from the rotation point to where the force acts perpendicular. So the lever arm for F would be L, and the lever arm for the weight of the box would be L/2. F*L = mg(L/2), and F = mg/2. Thanks, Doc!
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