The question for this week involves the pulley system in the photograph below. The question is how much force must be exerted on the free end of the rope to lift the weight at the bottom, including the weight of the attached pulley, which we will call W.
Reviewing the pulley configuration: beginning at the free end, the rope passes over the "free" pulley, under the pulley attached to the weight W, over the "fixed" pulley that is attached rigidly to the support rod, and finally supports the free pulley, as seen in the photograph.
It might require a force F=W to lift the weight. On the other hand, the general laws of pulleys suggest that if there are two ropes supporting the weight the force required to lift the weight might be W/2. However, this pulley system seems to be a bit more complicated than some others, so the force might be W/3. Or perhaps there might be some other solution.
Lifting the weight W by pulling on the free end of the rope with this pulley system requires a force equal to:
Click here for Answer #45 after January 1, 2001.
