The discussion clarifies the principle behind movable pulleys, specifically the trade-off between power and distance. It establishes that when using a movable pulley, the effort must move twice the distance of the load, illustrating the concept of mechanical advantage. The term "power" is deemed misleading; it should refer to "load" instead, as the actual weight lifted by the pulley. The relationship between input and output work is defined by the equation f_i * s_i = f_o * s_o, highlighting that an increase in output power results in a proportional decrease in distance moved.
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andrevdh said:Pulleys are used to lift objects. "Power" in this case refers to the weight that the pulley is lifting (the load suspended from it). The product of the load and the distance lifted is the work done by the lifting force. This energy is supplied by the mechanism hauling the rope (chain) in.
andrevdh said:No, instead of power you should read load, that is the actual weight that the pulley is lifting. The way that the term power is used in this problem is very misleading (and confusing especially in a Physics course as you have discovered) and I suspect that the author ment to use the term load. It would have been closer to the truth if the term "lifting or output power" was used. The reason why I suspect that this was his intention is that if one neglect energy losses the work input should be equal to the work output by the system:
f_i\ s_i = f_o\ s_o
This means that if the "output power" (load / output force) is four times the "input power" (input force) then the load can be lifted through only a quarter of the distance (speed) that the input force moves.