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Homework Help: Quick! force on the fulcrum of a lever?

  1. Apr 24, 2007 #1
    1. The problem statement, all variables and given/known data

    I have a lever problem, i wish to find the force on the fulcrum; how do i determine this force?

    http://www.UploadYourImages.com" [Broken]

    Fin = 80 N
    Fout= 21.5 N

    (yes, usually a lever is supposed to increase your power, but it represents a rowing oar)
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Apr 24, 2007 #2

    Chi Meson

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    No a lever does not increase your power, it increases your force. Power is W/t, and a machine cannot increase the work input. In reality all machines reduce the work since some energy is lost to friction.

    But to answer your question, first realize that "Fout" is the force from the oar on the water.

    Now you need to determine all the forces that are ON the oar. (Think Newton's 3rd).

    Then assume all forces on the oar are balanced (assuming the boat is not accelerating, much).
  4. Apr 24, 2007 #3
    so its just basically the difference between Fin and Fout. Thus in my case, the force on the oar would be Fin-Fout=58.8N; is that right?
  5. Apr 24, 2007 #4
    58.N in the direction of Fout i should say?
    Last edited: Apr 24, 2007
  6. Apr 24, 2007 #5
    anyone have an answer for this?
  7. Apr 24, 2007 #6
  8. Apr 24, 2007 #7


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    Yes, according to your diagram I would say the difference between Fin and Fout is the force on the fulcrum. But in my experience with oars, I would say Fin and Fout point in the same direction, hence it's the sum. Think only of the forces acting on the oar. Not on the water.
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