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geerky42

  • one year ago

Help Needed with Inertia...

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  1. geerky42
    • one year ago
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  2. Mashy
    • one year ago
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    ah... so the first thing you need to do is calculate the location of the centre of mass.. can you do that?

  3. geerky42
    • one year ago
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    Yeah, it's 1.95 m away from 1kg mass.

  4. geerky42
    • one year ago
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    Not sure what to do in next step...

  5. Mashy
    • one year ago
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    ok.. i won't check that then.. fine.. now answer this.. if i know that there is a mass that is connected to a string.. which has a length 'l'.. and i swirled it.. what would be the moment of inertia???

  6. Mashy
    • one year ago
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    |dw:1359715230549:dw|

  7. geerky42
    • one year ago
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    \(\large I = \dfrac{1}{3}ml^2\), right?

  8. Mashy
    • one year ago
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    noooOOO :O.. how did you get that? :O

  9. Mashy
    • one year ago
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    its a point mass.. imagine its a point mass!!

  10. geerky42
    • one year ago
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    Idk, it's a formula for end of rod, though this is what you asked for, sorry

  11. Mashy
    • one year ago
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    no.. what is the general formula for moment of inertia?? i think the concept itself is not clear to you.. huh?

  12. geerky42
    • one year ago
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    You mean \(\large I = ml^2\)?

  13. geerky42
    • one year ago
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    it's a general formula for inertia, i think.

  14. Mashy
    • one year ago
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    its \[\sum_{ }^{ } mR ^{2}\]

  15. Mashy
    • one year ago
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    thats the general formula.. and in my question .. since only one point mass is present.. you can say its just \[ml ^{2} \]

  16. geerky42
    • one year ago
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    So for my question, I just use the sum of inertia?

  17. Mashy
    • one year ago
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    so its basically summasation of all point mass times their distance from the axis of rotation squared.. so in your question.. you have 2 point masses.. so find each one's moment of inertia and sum it up

  18. Mashy
    • one year ago
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    and don't call it inertia.. its called moment of inertia :P

  19. Mashy
    • one year ago
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    inertia = resistance to change for linear motion moment of inertia = resistance to change for rotational motion

  20. geerky42
    • one year ago
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    ok I see. does this formula \(\displaystyle\int r^2 \text{d}m\) work too? I tired this way and I got lost.

  21. Mashy
    • one year ago
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    that is only if you have a rigid object.(continuos distribution of mass). but in your case its not a rigit object... its just 2 point masses.. !! so you can indivisually find their moment's of inertia about the rotational axis and sum them up..

  22. geerky42
    • one year ago
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    I see. Thanks!

  23. Mashy
    • one year ago
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    your welcome :)

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