Seems that like the story with the dollar and the hotel room, http://answers.yahoo.com/question/index?qid=20080404092048AAbWl3m , the answer is confussed by the premise that with a one to one tackle the load at the mast head is 200 lbs, when it would just be 100 lbs. All that is happening is that the load direction is being changed. Would it take a 200 lb line to hold the block at the mast head static? No, If you add tension yes, but then the difference is only the tension that is added is what you need to hold. Now when you add the new block and tackle while you have an advantage in the amount of line pulled you don't have an advantage in the weight moved. So the line would be holding 1/3 the mass of the weight. Check out: http://en.wikipedia.org/wiki/Pulley for a more complete explanation.

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