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Torque problem, please help

  1. Nov 9, 2008 #1
    A floodlight with a mass of 40 kg is used to
    illuminate the parking lot in front of a library.
    The floodlight is supported at the end of a
    horizontal beam that is hinged to a vertical
    pole, as shown. A cable thatmakes an angle of
    11◦ with the beam is attached to the pole to
    help support the floodlight. Assume the mass
    of the beam is negligible when compared with
    the mass of the floodlight.
    The acceleration of gravity is 9.81 m/s2 .

    a) Find the force FT provided by the cable.
    Answer in units of N.
    2056 N
    b) Find the horizontal force exerted on the
    beam by the pole. Answer in units of N.

    c) Find the vertical force exerted on the beam
    by the pole. Answer in units of N.


    I got a and b but for some reason I can't get c.
    My work.
    Fynet=0=Tsin11+Fy-mg where Fy is the vertical force exerted on the beam by the pole.
    Tsin11+Fy=mg
    392.4 +Fy=392.4
    Fy=0
    however, that doesn't work
    anyone has suggestions for part c?
     
  2. jcsd
  3. Nov 9, 2008 #2
    [tex]\sum\tau=\tau_1+\tau_2=r\vec{w}+r\vec{T}\rightarrow\vec{w}=-\vec{T}\sin(11\pi/180)\rightarrow\vec{T}=2057N[/tex].

    Then, we notice that [tex]\sin(11\pi/180)\cdot2057=392.5[/tex] and [tex]\vec{w}=392.4[/tex]. So, maybe it's just that 0.10N that they're worrying about? IDK.
     
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