Moment of intertia of wheel

  • Thread starter dannee
  • Start date
  • #1
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Homework Statement




i've attched a picture of the wheel, which need to calculate moment of intertia with respect to 8 rods.

i've tried to use stiener rule but it's not getting the answer,

moment of wheel is (m1*r^2)/2
moment of rod is (m2*r^2/3)

i use the rule i total = icm + mr^2

so it's 8*( (m1*r^2)/2 + (m2*r^2)/3 )

what am i missing?



Homework Equations



m1 = mass of wheel
m2 = mass of rod
r = length of rod

The Attempt at a Solution

 

Attachments

  • wheel.JPG
    wheel.JPG
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Answers and Replies

  • #2
Doc Al
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moment of wheel is (m1*r^2)/2
Revisit this formula.

so it's 8*( (m1*r^2)/2 + (m2*r^2)/3 )
There are 8 spokes but only 1 wheel.
 
  • #3
20
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that's right, 8 * 3(m2*r^2), i refer the moment of wheel is (m1*r^2)/2 and sum them,

but the correct answer is (3m2/8 + m1) * r^2
 
  • #4
Doc Al
Mentor
45,084
1,394
that's right, 8 * 3(m2*r^2), i refer the moment of wheel is (m1*r^2)/2 and sum them,
(1) Your formula for the moment of inertia of the wheel portion is incorrect.
(2) In your final result in post #1 you multiplied all terms by 8, thus counting the wheel 8 times.

but the correct answer is (3m2/8 + m1) * r^2
Double check that answer; looks like a typo.
 

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