The strong man can withstand the tension force exerted by two horses pulling in opposite directions. How would the tension compare if only one horse pulled and the left rope were tied to a tree? How would the tension compare if the two horses pulled in the same direction, with the left rope tied to the tree? Here's what I have. If one of the ropes was tied to the tree, wouldn't it basically be the same as when there were two horses pulling in opposite directions, because since the horse is pulling the person away from the tree, the tree is pulling in the opposite direction on the person. If two horses were pulling on the tree, then the tree once again would be pulling back in the opposite direction on the person, only this time twice as hard because it has to balance out the two horses now instead of one.