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Finding Center of Mass

  1. Oct 27, 2009 #1
    A thin rectangular plate of uniform areal density σ = 3.13 kg/m2 has length of 44.0 cm and width of 26.0 cm. The lower left hand corner is located at the origin, (x,y)= (0,0) and the length is along the x-axis.
    There is a circular hole of radius 7.00 cm with center at (x,y) = (16.00,11.00) cm in the plate

    Calculate the x-coordinate of CM of the plate.!?
    Calculate the distance of the plate's CM from the origin.!?

    for some odd reason i can figure out any other problem but this one if someone could help me out that would be great
  2. jcsd
  3. Oct 28, 2009 #2
    do you have to calculate it?
    you can hang it from two or more points to find the CM :-)
  4. Oct 28, 2009 #3
    yes i have to calculate it i dont even know where to start
  5. Oct 28, 2009 #4


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    Homework Helper

    Find the position vectors of the CM of rectangular plate and removed circular disc.
    Let M be the mass of plate and m be the mass of the disc.
    Position vector R1 of M = (022i + 0.13j). Mass M = σ*A. where A is the area of the plate
    Position vector R2 of m = (0.16i + 0.11j) Mass n = σ*a ,where a is the area of the removed circular disc.
    Then the position vector of CM of the remaining mass of the rectangular plate is
    R = (M*R1 - m*R2)/(M - m)
  6. Oct 28, 2009 #5
    If you know the moment of inertia at any two points, can you use the principal axis theorem to triangulate the CM?
    Bob S
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