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 €œtensioning pulley€ that rolls back and forth on rails, as shown in FIGURE EX7.21. 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?

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Cable 1.5 m Rail 2000 kg FIGURE EX7.21