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Homework Help: Quick questions

  1. Dec 25, 2005 #1


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    Two questions,
    a) how does pressure (in N/cm^2) on the cross section of a human bone change if the length (i'm assuming the length of the person) would increase 10 times ?
    b) How big would a giant have to be so it's legs can support a pressure of 1000 N/cm^2 with a cross section area of 8 cm^2 ? (1 kg = 10 N)
    ok, for b) i assumed it's just a matter of obtaining how much force would be generated, so it would be 8000 N , so the giant would be 800 kg. right?
    but how do i go about doing a) ?, i thought of assuming for example a 190 cm male would weigh about 80kg in average, which gives 800 kg after multiplying the height by 10. but i would still need cross section area for it. I'm sure there is a better way to do this.
    Thanks for any help.
  2. jcsd
  3. Dec 26, 2005 #2


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    You are leaving a lot unsaid. Do you mean that all linear distance are increased 10 times (so that cross section area is increased by 100 times and volume by 1000 times)? It's not clear to me why the pressure on a cross section would increase at all or why it would be a constant increase. Are you assuming a constant force on the increased cross section? If you were talking about the femur (leg bone), there would be a lot of weight increase above it that would result in a lot of force increase. If you are talking about a neck bone, there would be relatively little increase in force for a similar increase in cross section area. If you are talking about an ulna (forearm bone) while the forearm is lying on a table, there would not be any increase in force at all.
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