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Homework Help: Angle of twist of a gear relative to another

  1. Jan 5, 2017 #1
    1. The problem statement, all variables and given/known data
    why we need to consider 2 moment caused by the 85Nm in this question ? The question ask for the determine the angle of twist of gear A relative to D .

    2. Relevant equations

    3. The attempt at a solution
    Why shouldnt the angle of twist = (85)(0.4) / ( (0.5pi)( 0.015^4- 0.01^4)(75)(10^9) ) + (85)(0.25) / (0.5pi)(0.02^4)(75)(10^9) only ?

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  2. jcsd
  3. Jan 7, 2017 #2


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    Science Advisor

    I'm not quite sure I understand your question but the factor of 2 you removed is there to account for the fact there are two identical shaft sections, AB and CD.
    Without that 2 you're ignoring one of the hollow sections and your answer is the twist of A relative to C (or B relative to D).
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