If a block and tackle arrangement were rigged as shown in figure "G" in the illustration, the amount of force "P" required to hold the 394 pound load stationary would be __________. See illustration GS-0110.
• Identify how many supporting rope segments are actually carrying the load in figure G • Use the mechanical advantage (MA) formula: MA = Load / Effort (W / P) for an ideal, frictionless system • Remember that only rope parts that directly support the moving block or load count toward mechanical advantage
• Looking at figure G, which rope segments are pulling up on the moving block or load, and how many are there? • If the total load is 394 lbs and the number of supporting parts is N, what would the effort P be in a frictionless system? • After computing P = 394 / N, which of the answer choices is closest to that ideal value?
• Carefully trace the rope path from the fixed point to the free end labeled P so you don’t miss any supporting segments • Be sure you do not count rope segments that are just changing direction on a fixed block and do not attach to the moving block • After calculating P, compare the result to each option and think about small increases for friction that might exist in a real tackle
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