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Min force to open the water gate

  1. Feb 26, 2016 #1
    1. The problem statement, all variables and given/known data
    why Fr(Lp) = FB / 2 ??? can someone help to explain ?

    2. Relevant equations


    3. The attempt at a solution
    shouldn't it be 2FB = Fr(Lp) ? since FB act on 2 sides of the gate ...
     

    Attached Files:

  2. jcsd
  3. Feb 26, 2016 #2

    haruspex

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    It's Fb/2 because F acts at b/2 from the hinge. It only acts on one side.
    Fr acts at Lp from the hinge on the other side.
     
  4. Feb 26, 2016 #3

    BvU

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    Author sure has a funny way of drawing a 45 degree angle !
    And conspicuously does not draw a hint of a hinge at B.

    Furthermore, the horizontal line at 3 m is supposed to designate something sturdy that has water above and air below ? Quite something different from the liquid surface at 4.2 m; more like the stuff the gate itself should be made of. Deceptive drawing, incompetence, sloppiness ?
     
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