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    christinaschreiner's Avatar
    christinaschreiner Posts: 2, Reputation: 1
    New Member
    		  
    #1

    Oct 28, 2007, 06:37 PM
    Changing Your Center of Mass
    "To keep the calculations fairly simple, but still reasonable, we shall model a human leg that is .92m long (from hip joint) by assuming that the upper leg and the lower leg (including the foot) have equal lengths and that each of them is uniform. For a 70kg person, the mass of the upper leg would be 8.60kg, while that of the lower leg (including the foot) would be 5.25kg."

    Find the X AND Y COORDINATE of the center of mass of this leg, relative to the hip joint, if it is bent at the knee to form a right angle with the upper leg remaining horizontal.
    CaptainRich's Avatar
    CaptainRich Posts: 4,492, Reputation: 537
    Cars & Trucks Expert
    		  
    #2

    Oct 28, 2007, 06:45 PM
    https://www.askmehelpdesk.com/other-...board-b-u.html
    terryg752's Avatar
    terryg752 Posts: 197, Reputation: 4
    Junior Member
    		  
    #3

    Oct 31, 2007, 05:32 PM
    Suppose mass of upper leg is m1, lower leg m2

    Let length of each leg be L

    Centre of mass of upper leg is mid point of upper leg, coordinates (L/2, 0)
    Centre of mass of lower leg is mid point of lower leg, coordinates (L, -L/2)

    Masses are m1 and m2

    Centre of mass of masses m1 and m2 at these two points

    X = (m1 x1 + m2 x2)/(m1 + m2) = (m1 L/2 + m2 L)/(m1 + m2)

    Y = (m1 y1 + m2 y2)/(m1 + m2) =
    (0 m1 -m2 L/2)/(m1 + m2) = -m2 L/2/(m1+m2)

    Substitute values of L, m1, m2
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