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!

Find the deflection of the following points

  1. Nov 18, 2009 #1
    in this question

    Capture.JPG


    A1=8*10-4m2
    A2=5*10-4m2
    E=70*109Pa
    F1=-100*103N
    F2=75*103N
    F3=50*103N

    [tex]\sigma[/tex]=F/A
    [tex]\epsilon[/tex]=[tex]\sigma[/tex]/E = [tex]\frac{F}{A*E}[/tex]
    [tex]\delta[/tex]=[tex]\epsilon[/tex]*L = [tex]\frac{F*L}{A*E}[/tex]


    [tex]\delta[/tex]B = [tex]\frac{F1*1.75}{A1*E}[/tex] + [tex]\frac{F2*3}{A1*E}[/tex] + [tex]\frac{F3*3}{A2*E}[/tex] = 5.1785*10-3m


    but thats not right


    even looking at the second answer
    i thought

    [tex]\delta[/tex]D=[tex]\delta[/tex]B + [tex]\frac{F3*1.5}{A2*E}[/tex]
    but if i plug in THEIR answer for [tex]\delta[/tex]D i get 2.924mm and not the 5.7 they say
     

    Attached Files:

    Last edited: Nov 18, 2009
  2. jcsd
  3. Nov 18, 2009 #2

    djeitnstine

    User Avatar
    Gold Member

    The forces used in the second and third terms of your equation for [tex]\delta_B[/tex] are wrong. You have to take a cut at each point, draw a free body diagram and sum the forces for equilibrium
     
  4. Nov 19, 2009 #3
    if so, then why not for the 1st term as well?
     
  5. Nov 19, 2009 #4
    for a similar problem, but where the diameter was constant and the E was different for the 2 parts, i did exactly that and it worked.
     
  6. Nov 19, 2009 #5
    i got it, thankls for the help
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Find the deflection of the following points
Loading...