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Homework Help: Static hydraulics, calculate water depth

  1. Dec 3, 2011 #1
    1. The problem statement, all variables and given/known data
    Refer to Figure 3. A steel box (250 mm x 250 mm x 250 mm) is placed at the bottom of a tank. If the pressure on the top surface is 10000 Pa, what is the water depth in the tank?

    a. 1019 mm
    b. 251.02 mm
    c. 1269 mm

    water density: 1000 kg/m3
    gravity: 9.81

    2. Relevant equations

    3. The attempt at a solution

    if the pressure on the top surface f the box is 10,000pa, then by rearranging the formulae P=pgh you get:

    10,000= 1000 x 9.81 x h

    solving for h:

    h = 0.981 meters

    adding the depth at the top of the box to the height of the box to find the final depth of the tank=

    981mm + 250mm = 1231mm

    however this is not the correct answer?
  2. jcsd
  3. Dec 3, 2011 #2


    User Avatar
    Science Advisor
    Homework Helper

    escobar147: You simply made an obvious algebra mistake. Try again. Also, always leave a space between a numeric value and its following unit symbol. E.g., 250 mm, not 250mm. Also, the unit symbol for pascal is Pa, not pa. Lowercase p means pico. It should be 10 000 Pa.
  4. Dec 4, 2011 #3
    omg i have just realized my mistake. i incorrectly re-arranged the formula, the actual answer is this:

    P = pgh

    10,000 = 1000 x 9.81 x h

    10,000 = 9810 x h

    10,000/9810 = 1.01936 meters

    1.01936 meters + 250 mm

    = 1.269 meters.

    thanks for your help nvn i appreciate it!
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