Question: The cable cars in San Francisco are pulled along their tracks by an underground steel cable that moves along at 9.5mph. 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 the cable stretches by up to 100ft 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 diagram <http://img245.imageshack.us/img245/1350/cablecarib9.jpg>. A 2000kg block is attached to the tensioning pulley's cart, via a rope and pulley, and is suspended in a deep hole. Q:What is the tension in the cable car's cable My question is: 1. Since the cable is not accelerating can it be treated as if it is just fixed? 2. Is the 9.5 mph, 100ft stretching and the diameter of the pulley relevant information. It seems to me that most of that is not necessary to solving this problem. When i first attempted to solve this it seemed that the tension force that the cable would be feeling would be equal in magnitude to the force applied to the cable car by the 2000kg block. Is this reasoning correct?