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Homework Help: Estimate the pressure exerted on a floor

  1. Jan 9, 2017 #1
    1. The problem statement, all variables and given/known data
    3. (I) Estimate the pressure exerted on a floor by (a) one pointed chair leg (66 kg on all four legs) of 2 area  0.020 cm , and (b) a 1300-kg elephant standing on one foot   2 area  800 cm .

    2. Relevant equations

    3. The attempt at a solution

    I know the solution. But I don't understand why in (a) we used the mass of one leg and on (b) we used the mass of the whole elephant..even though the elepahnt was standing on one foot just like the chair was standing on one leg.
  2. jcsd
  3. Jan 9, 2017 #2


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    Well, the problem statement dictates it. Striking that an elephant exercises less pressure with one foot than a chair with 4 !

    It explains nicely why our wooden floor only has lots of imprints from the visiting ladies with stiletto heels and none from the elephants :smile:

    I do have trouble reading off the areas, though. ##0.02## cm2 doesn't feel right.
  4. Jan 9, 2017 #3
    The wording for the chair leg is kind of unclear. There are two possibilities: 1) There is a total of 66 kg spread out equally over 4 of the chair legs, or 2) each chair leg supports 66 kg. It appears that each leg is supporting 66 kg, based on where you said, "in (a) we used the mass of one leg".
  5. Jan 9, 2017 #4
    All 4 legs support 66 kg so one leg support 1/4 x 66
  6. Jan 9, 2017 #5
    I mean in the answer he used 1/4 times 66 to find the mass on one leg.

    But in (b) he used the whole mass of the elephant while it was on one foot..why he didn't use 1/4 times mass of the elephant? considering that the elephant has 4 legs?
  7. Jan 9, 2017 #6
    It says the elephant is standing on one foot.
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