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: Young's modulus - calculating delta L

  1. Nov 7, 2009 #1
    1. Consider a steel guitar string of initial length L=1.00 meter and cross-sectional area A=0.500 square millimeters. The Young's modulus of the steel is Y=2.0 \times 10^{11} pascals. How far ( Delta L) would such a string stretch under a tension of 1500 newtons?
    Use two significant figures in your answer. Express your answer in millimeters.




    2. Y = kL/A
    k = YA/L




    3. k = YA/L = (2*10^11 N/m^2)*(.0005m^2) / 1m = 1*10^8 N/m

    deltaL = F/k = 1500N/(1*10^8 N/m) = 1.5*10^-5m = .015 mm

    I made a mistake with units somewhere but I can't spot it.
     
  2. jcsd
  3. Nov 7, 2009 #2
    Remember that when converting from square millimeters to square meters, you have to square the factor that you are changing by.

    Since 1mm = 0.001m, 1mm2 = 0.001m * 0.001m = 0.000001m2

    Your problem is that you are dividing by 0.0005m2 instead of 0.0000005m2, so your answer is exactly three orders of magnitude too small.
     
  4. Nov 7, 2009 #3
    Thanks!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...