1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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


    User Avatar
    Science Advisor
    Homework Helper
    2017 Award

    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 ?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted