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Math Help - Relative accelleration Problem

  1. #1
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    Relative accelleration Problem

    Iam having some difficulty with this one iff some one could help.
    What is the accelleration of point D (the centre)
    Attached Thumbnails Attached Thumbnails Relative accelleration Problem-lastscan2.jpg  
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  2. #2
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    Could you please give the problem statement in full?
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  3. #3
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    There is a disk,it is ONE piece.It has a large diam and small diam.
    The small dia rolls on a desk to the right.The large dia section does not touch the desk,but has a tangential acceleration as shown.
    That is all that is known .
    Find the accelleration of centre of the disk.
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  4. #4
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    I think the thing to do is to find out the angular acceleration \alpha. Once you do that, you employ the (assumed) condition that the inner wheel rolls without slipping in order to translate the angular acceleration to linear acceleration. I do not think you have correctly computed the angular acceleration, although you have the correct general equation there:

    a_{\text{tan}}=r\,\alpha.

    Try computing that again. What do you get?
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  5. #5
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    Thanks for that ,appreciated,I worked it out
    ans is 15m/s^2 to the left

    5m/s^2=r alpha
    where r =(2-1.5) /2 (because where disk touches desk accell is 0 in the x directions) ie 5m/s^2 wrt desk.
    alpha=20
    accell of ctr = 20*1.5/2
    Last edited by heatly; October 13th 2010 at 05:30 AM.
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  6. #6
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    Hmm. Not sure I agree. To start out, you'd have

    5.0 m/s^2 = (1 m)(alpha), which implies alpha = 5.0 1/s^2. Then how would you continue?
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  7. #7
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    oops,fixed up now,thanks
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  8. #8
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    r =(2-1.5) /2
    That is incorrect. You need to measure the radius from the center of both concentric circles to the outermost edge. Use the 1m I used.
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  9. #9
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    Ok,I'll look into it thansk.
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