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Homework Help: Rigid Rod

  1. Apr 3, 2006 #1
    Rigid rods of negligible mass lying along the y axis connect three particles (Fig. P10.20). The system rotates about the x axis with an angular speed of 1.20 rad/s.

    (a) Find the moment of inertia about the x axis.

    So isnt the moment of inertia given by the sum of mr so..

    (4kg)(3m)+(2kg)(-2m)+(3kg)(-4m) = -4?
     

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  2. jcsd
  3. Apr 3, 2006 #2

    Doc Al

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    Staff: Mentor

    That should be the sum of [itex]m r^2[/itex].
     
  4. Apr 3, 2006 #3
    so (4)(3^2)+(2)(-2^2)+(3)(-4^2) = (4)(9)+(2)(4)+(3)(16)=36+8+48=92?
     
  5. Apr 3, 2006 #4

    Doc Al

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    Staff: Mentor

    Yes, in units of kg-m^2.

    (Realize that r is the distance from the axis, so it should be positive.)
     
    Last edited: Apr 3, 2006
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