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Homework Help: Simple Static Pressure problem, need help with units

  1. Sep 19, 2011 #1
    1. The problem statement, all variables and given/known data
    Hi i'm having trouble solving this physics problem if anyone can help it would be greatly appreciated !

    Static pressure problem: A bathtub contains water to a depth of 20 inches. Determine the pressure at the bottom of the bathtub in both [psia] and [psig] (a being absolute pressure and g being gauge pressure)

    2. Relevant equations
    im using P=pgh

    3. The attempt at a solution
    what i've tried doing was to find gauge pressure first: P=pgh=(1.94slug/ft^3)(32.2ft/s^2)(1.67ft). I got the 1.67 feet from converting 20 inches to feet. the answer i get is 104.11slug/s^2 but they want it in psi or lb/in^2 and i am having trouble converting these units =[
  2. jcsd
  3. Sep 19, 2011 #2
    Why don't you just convert the initial 20 inches to meters then solve for the standard SI units?
  4. Sep 19, 2011 #3
    Well the problem is that i don't know how to get rid of the /s^2 in my final answer and even if i use the standard SI units ill still come up with an answer that has /s^2
  5. Sep 19, 2011 #4
    That's the acceleration…s^2 is an SI unit.
  6. Sep 19, 2011 #5

    look at the definition of what a pound actually is (in terms of units). That should fix things.
  7. Sep 19, 2011 #6


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Instead of using different unit systems, 1 cu. ft. of fresh water weighs about 62.4 pounds. Knowing that number, you should be able to find psi given the depth of water in the bath tub.
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