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Homework Help: Fluid Dynamics - Hydrostatic Pressure #2

  1. Oct 31, 2015 #1
    1. The problem statement, all variables and given/known data
    a Flat rectangular door in a mine is submerged from one side in water. The door dimensions are 2m high, 1m wide and the water level is 1.5m higher than the top of the door. The door has two hinges on the vertical edge, 160mm from each corner and a sliding bolt on the other side in the middle. Calculate the forces on the hinges and sliding bolt.
    (Hint: consider the door from a side view and from a plan view respectively and take moments about a point each time.)
    Answers: 8.327kN; 16.15kN; 24,525kN

    2. Relevant equations

    3. The attempt at a solution
    i am able to calculate the pressure at the sliding bolt but i dont know how to approach the problem of the hinges, please help me to understand this concept.

    Sliding bolt:
    Fsb = p(water density) g 'y A(door) / 2 'y = 2/2 + 1.5
    = (1000)(9.81)(2.5)(2x1) / 2 'y = 2.5
    = 24.525 kN

    now i thought that to get the answer to the hinges you simply just change 'y to the desired distance, 'y = 1.5+ 0.160
    and for the second hinge 'y = 1.5 + ( 2 - 0.160 )

    the ansers i get is not correct, the text book has these questions as excercises after each module.

    i hope to hear from you soon.

    Lukas van Rooyen
  2. jcsd
  3. Oct 31, 2015 #2


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    The hinges and the sliding bolt keep the water pressure from pushing the door our of its frame. The force on the hinges or the sliding bolt is not just ρgh * Adoor

    Remember to use the Hint given in the Problem Statement.
  4. Oct 31, 2015 #3
    thanks for the feedback

    i tried all possible angles to tackles this problem but i cant, so if someone can help me and show me step by step with notes i would really appreciate it.

  5. Oct 31, 2015 #4


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    Sorry, but the Rules of PF state that you must do your own work.

    If you care to share your best attempt at solving this problem, perhaps you might get a helpful suggestion which will lead you to a solution.
  6. Nov 1, 2015 #5

    i am not asking for the answer i have the answer, i am asking to explain how to get to the answer i dont grasp the concept, shees what a hasstle for some help on this site, luckily i found CHEGG.com there i even speak to a tutor who explains to me the concept.

    but yey well thanks for wasting my time, will not use this website again.

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