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Center Gravity and Moment of Inertia

  • Thread starter ymehuuh
  • Start date
  • #1
19
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Homework Statement


Four objects are held in position at the corners of a rectangle by light rods as shown in the figure below. The mass values are given below.
M1 (kg) M2 (kg) M3 (kg) M4 (kg)
3.50 1.50 3.90 1.70
p8-29alt.gif

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

(b) Find the moment of inertia of the system about the y axis.

(c) Find the moment of inertia of the system about an axis through O and perpendicular to the page.

Homework Equations



Center of Gravity: sumM1*X1+M1*X2.../M1+M2...

The Attempt at a Solution



I found the center of gravity for the x axis to be .037736...how do I find the moment of inertia with that information?
 

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Answers and Replies

  • #2
LowlyPion
Homework Helper
3,090
4
You need to find the x and y CoM.

Knowing that then the moment I about the CoM is Σmr2.

The axes are simpler in that for

I_x = Σm_i*y_i2

I_y = Σm_i*x_i2
 
  • #3
19
0
Oh, I reversed the two and that's why I got it wrong. Thanks.
What would I use for part c?
 
  • #4
LowlyPion
Homework Helper
3,090
4
Oh, I reversed the two and that's why I got it wrong. Thanks.
What would I use for part c?
What are the distances to each corner from O to each mass?

I_o = Σmr2

It's made a little easier by Pythagoras, so be sure and thank him.
 
  • #5
19
0
what are the distances to each corner from o to each mass?

I_o = Σmr2

it's made a little easier by pythagoras, so be sure and thank him.
perfect! Thanks!!
 

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