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Math Help - Rotating shaft

  1. #16
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    Re: Rotating shaft

    mechanical engineering. I follow your moments from the point A as this is what I have. Its the next part I don't know how to get from there to my answer of F1=6 and F2 =2. This is where I become unstuck...
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  2. #17
    Junior Member
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    Re: Rotating shaft

    Yeah I 100% have the same as you for 0.5F1-1.5F2-2Rb
    How do I get from that though to the final answer of F1=6 and F2=2
    Been at this for days and cant clear this final hurdle to finish this up.....
    Currently Iam no further on than where I started....
    Last edited by Jock; February 27th 2014 at 10:53 AM.
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  3. #18
    MHF Contributor ebaines's Avatar
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    Re: Rotating shaft

    You have two equations in two unknowns, F_1 and F_2:

    \sum F = 0 = R_a + R_b -(F1 + F_2)

     \sum T_a = 0 = 0.5F1 + 1.5F_2- 2R_b

    Using a technique you learned in the 9th grade: rearrange the first equation so that F_2 is by itself:

    F_2 = R_a + R_b - F1

    and subsutite for the F_2 term in the second equation:

    0 = 0.5F1 + 1.5 (R_a + R_b - F1)- 2R_b = -F_1+1.5R_a-0.5R_b

    and rearrange to solve for F_1:

    F_1=1.5R_a-0.5R_b = 1.5(5N)-0.5(3N) = 6N

    So that's F_1. Now use this value of F_1 back in the earlier equation for F_2:

    F_2 = R_a + R_b - F1 = 5N + 3N - 6N = 2N.
    Thanks from Jock
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