Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Center of gravity

  1. Apr 19, 2007 #1
    1. The problem statement, all variables and given/known data
    A unifrom disc A of radius 2m is cut as shown in the image. The cut out is also a disc of radius 1m. Find the distance of the two center of gravity before and after the paper disc is cut.

    http://crossfacer.com/circle.jpg [Broken]
    2. Relevant equations


    3. The attempt at a solution

    Mass of the disc is proportional to its area.
    so mass of disc A=2^2pi=4pi units
    mass of disc being cut out=1^2pi=pi units

    Let x be the distance between the two centers of gravity.

    This question is quite difficult for me. I don't have much confidence on my answer.:tongue2: May anyone try it?:smile:
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Apr 19, 2007 #2


    User Avatar
    Homework Helper

    Your answer looks correct in my book.

    You assume the homogeneity of the disc, and thus mass is proportional to the area. You know that together, they produce a center of gravity balanced at the center of disc A, and your equations reflect that.
  4. Apr 19, 2007 #3
    I feel like my answer is not correct:frown:. I guess x should be about 0.5.
  5. Apr 19, 2007 #4
    well to check maybe you could use same methods with your new result and cut out identical hole in left half. I think it will end up in the middle again.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook