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Pressure, force, area

  1. Dec 24, 2016 #1
    1. The problem statement, all variables and given/known data
    Pressure is 8 kPa, mass is 10 kg, length of one side of rectangle is 1.2 m
    Find width of rectangle

    2. Relevant equations
    P=F/A
    N = kg * m * s^-2



    3. The attempt at a solution
    8kPa = (10kg * 10m/s) / (1.2 m * X m) /// X is the unknown width

    8000Pa = 100N / 1.2X m^2

    8000Pa * 1.2m * Xm = 100 N

    X m = 100N / 9600 m * N/m^2

    X m = 0.01 m

    Wrong -- width won't be 0.01 m!
     
  2. jcsd
  3. Dec 24, 2016 #2
    are you sure there is no given acceleration ?
     
  4. Dec 24, 2016 #3

    gneill

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    Staff: Mentor

    Hi rrrrrr, Welcome to Physics Forums!

    Your attempt at solution was logical given a likely interpretation of the given information in the problem statement, yet you claim that the answer you arrived at was wrong. Perhaps there's something missing from the problem statement that could shed light on this?

    While we can guess at a likely scenario, it would be better if you could provide explicit detail so there's no confusion. Always endeavor to make your statement of the problem as clear and complete as you can.
     
  5. Dec 24, 2016 #4
    Thank you for responding - there was nothing about acceleration.
     
  6. Dec 24, 2016 #5

    gneill

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    Staff: Mentor

    What is your basis for saying that the width cannot be 0.01 m? You must have more information of some kind...
     
  7. Dec 24, 2016 #6
    Thank you for responding. The question is from a test in an introductory physics course in 9th grade. What we wrote here is our guess at how to solve it.
    The whole question just read that "A body of rectangular shape applies to a surface a pressure of 8kPa. The mass of the body is 10 kg and its length is 1.2 m.
    A) What is the width of the body?
    B) How will the pressure that the body exerts on the surface change if the width of the body is doubled?
     
  8. Dec 24, 2016 #7

    gneill

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    Staff: Mentor

    Okay! That's a much better problem statement :approve:

    With that information it seems that your solution to part (A) for the width is fine.
     
  9. Dec 24, 2016 #8
    Thank you very much. We weren't sure of the result.
     
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