You are using tackle number 5 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. What is the mechanical advantage of this rig?
• Count the number of parts of line actually supporting each moving block (tackle 5 and tackle 8) • Remember that if the hauling part moves instead of being secured, it still contributes as one part of line • For combined tackles, the overall mechanical advantage is the product of the individual advantages
• First, find the mechanical advantage of tackle 5 alone by carefully counting how many rope segments are lifting its moving block • Next, determine the mechanical advantage of tackle 8 by the same method • Then think about what happens when the hauling part of tackle 5 is attached to the weight hook (w) of tackle 8: how does one tackle’s pull act on the other?
• Verify you are only counting line segments that directly support the moving block and load, not those just changing direction at a fixed point • Confirm whether there is or is not a fall secured to the becket that would change the count by one • Before choosing, re-check that the final mechanical advantage equals the product of the two tackles’ advantages, not their sum
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