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Four rods of equal mass m each , Ab , BC , CA , DB are placed as shown. The moment of inertia of the system about B perpendicular to the plane ABC is (AB=a)

  • one year ago
  • one year ago

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  1. Yahoo! Group Title
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    |dw:1360169550988:dw|

    • one year ago
  2. Yahoo! Group Title
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    @JamesJ

    • one year ago
  3. JamesJ Group Title
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    Obviously break down the problem rod by rod.

    • one year ago
  4. JamesJ Group Title
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    And if you're really stuck, you're just going to integrate rod by rod.

    • one year ago
  5. Yahoo! Group Title
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    I (BC) = ma^2/6 ryt ?

    • one year ago
  6. shubhamsrg Group Title
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    Its basically a maths ques, you just need to find rod lengths, after doing that you just have to calculate moment of inertia of each rod about B and add all

    • one year ago
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    Yup . i Have Calculated the length of rods BC = a/sqrt(2) , AC = a/sqrt(2) , DB = (sqrt2) * a / sqrt3

    • one year ago
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    I (BC) = ma^2/6 ryt ?

    • one year ago
  9. shubhamsrg Group Title
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    yep

    • one year ago
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    I (DB) = ma^2/18 ?

    • one year ago
  11. shubhamsrg Group Title
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    won' that be (2/9)ma^2

    • one year ago
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    Hw ?

    • one year ago
  13. shubhamsrg Group Title
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    |dw:1360246728479:dw|

    • one year ago
  14. Yahoo! Group Title
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    I (DB) = M L^2 / 3 * sin^2 30 ryt ?

    • one year ago
  15. shubhamsrg Group Title
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    why sin ?

    • one year ago
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    |dw:1360246891927:dw|

    • one year ago
  17. shubhamsrg Group Title
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    I don;t think angle matters

    • one year ago
  18. shubhamsrg Group Title
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    For calculation of I,

    • one year ago
  19. shubhamsrg Group Title
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    Because the axis is perpendicular to plane, the rod will make 90 degrees with the axis, doesn't matter how it is placed.

    • one year ago
  20. shubhamsrg Group Title
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    Do you have the final ans ?

    • one year ago
  21. Yahoo! Group Title
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    Yup 25 M a^2 / 18

    • one year ago
  22. shubhamsrg Group Title
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    <Lets see if we get that by my method>

    • one year ago
  23. shubhamsrg Group Title
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    So DB = 2M a^2 /9

    • one year ago
  24. shubhamsrg Group Title
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    And AC = ma^2/6 + 3ma^2/6 = 2ma^2 /3

    • one year ago
  25. shubhamsrg Group Title
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    So sum = ma^2 (2/3 + 2/9 + 1/6) = 19/18ma^2

    • one year ago
  26. shubhamsrg Group Title
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    hmm, okay doesn't match

    • one year ago
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    i think that angle matters

    • one year ago
  28. shubhamsrg Group Title
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    Wait I missed AB

    • one year ago
  29. shubhamsrg Group Title
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    AB = ma^2 /3 Sum = 25/18

    • one year ago
  30. shubhamsrg Group Title
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    Got it! B|

    • one year ago
  31. Yahoo! Group Title
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    But Hw Did u Claculate I (AC) ??

    • one year ago
  32. shubhamsrg Group Title
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    calculate about C, then B

    • one year ago
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    Ok...got it....:)

    • one year ago
  34. shubhamsrg Group Title
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    "Angle will not matter here" ;)

    • one year ago
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