You are using tackle number 6 as shown in illustration D029DG below to lift a weight. The hauling part of this tackle is bent to the weight hook (w) of tackle number 8. Disregarding friction, what is the mechanical advantage of this rig?
• Mechanical advantage (MA) of a tackle equals the number of rope parts directly supporting the moving block(s), when friction is neglected. • In a compound tackle, the overall MA is the product of the MAs of the individual tackles. • Pay attention to how the hauling part of tackle 6 is attached to the weight hook (w) of tackle 8, and which blocks move with the load.
• For tackle 6 alone, how many rope segments actually lift its moving block (the one attached to the weight)? Does the hauling part count? • For tackle 8 alone, if its weight hook is being pulled instead of hanging a dead weight, how many supporting parts are acting on that hook? • Once you know the MA of each separate tackle from the illustration, how do you combine them when one tackle is pulling on the hook of the other?
• Carefully count only the rope parts that change length with the load in each tackle; ignore any parts that are fixed to a support. • Verify whether the standing part is at the fixed or moving block in each tackle, since that affects the MA by one. • Before choosing an answer, recompute: MA (tackle 6) × MA (tackle 8) and see which option matches.
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