1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: A little help please

  1. Jan 4, 2005 #1
    Im stuck on this one and its driving me a bit mad :confused:

    Here is what I have so far......

    Calculate the tensile stress in a nylon fishing wire of diamater 0.36mm which a fish is pulling with a force of 20 N.

    What I get:
    Stress = Force / Area

    Stress = 20 / π*(0.18x10^-3)^2

    Stress = 20 / 1.02x10^-7

    Stress = 1.96x10^8 Pa


    OR

    Area = π*(0.18)^2 mm
    Area = 1.02x10^-1 mm
    Area = 1.02x10^-4 m

    Stress = 20 / 1.02x10^-4

    Stress = 1.96x10^8 Pa

    Stress = 1.96x10^5 Pa


    WHEREAS it should be:

    Stress = 1.96x10^6 Pa


    Could somebody tell me what the answer is and PLEASE tell me how it was supposed to be worked out. This isnt really for homework per say, as its just a question I seen while working far ahead of everyone and it struck my curiosity.
     
  2. jcsd
  3. Jan 4, 2005 #2

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    Stress=Force/Area
    Force=20N
    [tex]A=\frac{\pi d^{2}}{4}\sim\frac{3.14\cdot(0.36mm)^{2}}{4}\sim 1.01\cdot 10^{-1}mm^{2}=1.01\cdot 10^{-7}m^{2} [/tex]
    [tex]Stress\sim\frac{20N}{1.01\cdot 10^{-7}m^{2}}\sim 1.97\cdot 10^{8}Pa [/tex]

    Daniel.
     
    Last edited: Jan 4, 2005
  4. Jan 4, 2005 #3

    learningphysics

    User Avatar
    Homework Helper

    Hmmm I get 1.96x10^8 Pa.

    Remember when converting areas that
    [tex]1mm=10^{-3}m[/tex] but
    [tex](1mm)^2=(10^{-3})^2m^2[/tex]
    so
    [tex]1mm^2=10^{-6}m^2[/tex]

    So your second answer should also come out to 1.96x10^8 Pa.
     
    Last edited: Jan 4, 2005
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook