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Find the deflection of the following points

  1. Nov 18, 2009 #1
    in this question



    [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

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


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    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
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