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Pressure of person on chair Question

  1. May 2, 2010 #1
    1. The problem statement, all variables and given/known data

    A 67 kg person sits on a 3.6 kg chair. Each leg of the chair makes contact with the floor in a circle that is 1.4 cm in diameter.


    2. Relevant equations
    p= M/V
    P= F/A
    Pg = P - Pat
    Pat = 1.01 x 105 N/m2


    3. The attempt at a solution
    I figured out the area of the circle using the pi r squared formula. This came out to be 1.54-4
    But I can't figure out how to finish the problem. Just looking for any advice on what to do next. I thought I should figure out the force by using W=mg formula which I tried but my answer for pressure was larger. Which I felt wasn't right
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
    Last edited: May 2, 2010
  2. jcsd
  3. May 2, 2010 #2
    How many legs does the chair have?
     
  4. May 2, 2010 #3
    It doesn't say how many legs the chair has. So I believe we should assume that the chair has 4 legs
     
  5. May 2, 2010 #4
    Then if you did divide the force of gravity by 4 times the area of one leg, I wouldn't know what was wrong with it.
     
  6. May 2, 2010 #5
    Use the total area of the legs. The weight is distributed over the 4 legs.
     
  7. May 2, 2010 #6
    Here is the question again. I don't understand it?

    A 67 {\rm kg} person sits on a 3.6 {\rm kg} chair. Each leg of the chair makes contact with the floor in a circle that is 1.4 {\rm cm} in diameter.

    Here is what they want me to find - Find the pressure exerted on the floor by each leg of the chair, assuming the weight is evenly distributed.

    Here are the equations that might be helpful to solve this problem

    p= M/V (density formula)
    P= F/A (pressure formula)
    pg= P - Pat (gauge pressure formula)
    at = 1.01 x 105 N/m2

    This is what I did?

    I found the Area by using pi r2

    Here is what I need help with?

    What should I do next. I thought I could find force by using the formula W=mg. But that didn't work my pressure answer was a big number
     
  8. May 2, 2010 #7
    It should work. Use W=mg to find the force, and P=F/A to find the pressure. You should get a big number, because the area of all the legs combined is a very small compared to a square meter. (and the pressure you get will be in Newtons per square meter)

    If you still get a wrong answer give your complete calculation.
     
  9. May 2, 2010 #8
    Thank you. That really helped
     
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