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Homework Help: Tension & Torque

  1. Nov 1, 2007 #1
    A thin horizontal bar AB of negligible weight and length L is pinned to a vertical wall at A and supported by B by a thin wire BC that makes an angle (theta) with the horizontal. A weight W can be moved anywhere along the bar as defined by the distance x from the wall.
    a) Find the tension T as a function of x
    b) Find the horizontal and the vertical components of the force exerted on the bar by the pind at A.
    c) With W = 315N, L = 2.76 m, and (theta) = 32deg, find the maximum distance x before the wire breaks if the wire can withstand a maximum tension of 520N.

    what i did was

    clockwise torques = counterclockwise torques since system is stationary

    cw torques: W
    ccw torques: T

    Wx = TL
    T = Wx/L

    ΣFx = 0
    Tx = Fax
    Tx = Tcos(theta)
    Fax = Wcos(theta)/L

    ΣFy = 0
    Ty = Fay
    Ty = Tsin(theta)
    Fay = Wxsin(theta)/L

    is this correct so far?
    if so I'm not sure how to solve for x using the angle (theta)
  2. jcsd
  3. Nov 1, 2007 #2
    I figure T = sqrt[(Tcos(theta))^2+(Tsin(theta))^2]
    Wx/L = sqrt[(Tcos(theta))^2+(Tsin(theta))^2]
    x = sqrt[L^2((Tcos(theta))^2+(Tsin(theta))^2)/w^2]

    then plugging in the numbers given I got x = 3.98 m.

    Is this correct?

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