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    mattmravunac's Avatar
    mattmravunac Posts: 4, Reputation: 1
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    #1

    Mar 13, 2013, 10:09 PM
    Physics Center Mass and Transitional Motion
    Suppose two friends, with masses m2 = 1.3 m1, are on a perfectly smooth, frictionless, frozen lake.
    They are both holding the end of a rope of length Lo .

    A) Find the position of the center of mass, in terms
    of Lo , from the smaller person.

    B) If the two pull half of the rope in such that the
    final length of the rope is L = Lo/2, find the new
    position of the center of mass from the smaller
    person.

    C) Find the distance each person moves from their original positions.
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Mar 14, 2013, 05:51 AM
    Please show us what you have done to try and solve these problems, and then we can help you wheer you get stuck. Keep in mind that the center of mass is that point on the rope where the distance to M1 times the mass M1 equals the distance to M2 times the mass M2.
    alpal24's Avatar
    alpal24 Posts: 1, Reputation: 1
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    #3

    Mar 14, 2013, 11:13 AM
    I need help with this one to. I got A and B but I am not really sure how to do C? Could you maybe help me set it up?
    mattmravunac's Avatar
    mattmravunac Posts: 4, Reputation: 1
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    #4

    Mar 14, 2013, 11:54 AM
    I know that
    X2=Lo and m2=1.3m1 and have the equation
    Xcm=(m2X2) / (m1+m2)
    I am just know sure how to go about it from this step
    hrab's Avatar
    hrab Posts: 4, Reputation: 2
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    #5

    Mar 14, 2013, 12:25 PM
    Xcm=(1.3m1*Lo)/(2.3m1)
    hrab's Avatar
    hrab Posts: 4, Reputation: 2
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    #6

    Mar 14, 2013, 12:26 PM
    So... its 0.57Lo=Xcm
    mattmravunac's Avatar
    mattmravunac Posts: 4, Reputation: 1
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    #7

    Mar 14, 2013, 02:44 PM
    Thank you!
    For part 2 would I just need to take the .057Lo/2? Which would give me .29 (?) or would I need to go about it like a completely new problem?
    hrab's Avatar
    hrab Posts: 4, Reputation: 2
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    #8

    Mar 14, 2013, 02:53 PM
    I think you need to set x1=Lo/4 and x2=3/4(Lo). And plug everything in and solve
    hrab's Avatar
    hrab Posts: 4, Reputation: 2
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    #9

    Mar 14, 2013, 02:59 PM
    So your cm will be half as far towards the heavier person. . 57/2=.285 .285+.25=Xcm if Lo/2
    mattmravunac's Avatar
    mattmravunac Posts: 4, Reputation: 1
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    #10

    Mar 14, 2013, 03:41 PM
    why would I need to set x1 to Lo/4 (?) if half the rope is gone then wouldn't that just be equal to Lo/2 and then X2 would be set to (1.3m1Lo)/2 (?)

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