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Homework Help: Tension in a cable car's cable

  1. Jun 18, 2008 #1
    The cable cars in San Francisco are pulled along their tracks by an underground steel cable that moves along at 9.5 mph. The cable is driven by large motors at a central power station and extends, via an intricate pulley arrangement, for several miles beneath the city streets. The length of a cable stretches by up to 100 ft during its lifetime. To keep the tension constant, the cable passes around a 1.5-m-diameter "tensioning pulley" that rolls back and forth on rails, as shown in the figure. A 2000 kg block is attached to the tensioning pulley's cart, via a rope and pulley, and is suspended in a deep hole.

    What is the tension in the cable car's cable?

    T[tex]_{b on a}[/tex]=T[tex]_{a on b}[/tex]

    I just don't even know where to start. I know that it's not accelerating, so Net Force=0 but I still can't figure out where to go from here. If I could just get pointed in the right direction, that'd be great! Thanks so very much!

    Attached Files:

  2. jcsd
  3. Jun 18, 2008 #2

    Doc Al

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    Staff: Mentor

    Hint: Treat the cart and pulley as a single system. What forces act on it?
  4. Jun 18, 2008 #3
    The tension of the hanging mass and the normal force of the rail on the cart, and the tension from the rope in the pulley?
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