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 254 pound load stationary would be __________. See illustration GS-0110.
• How to determine mechanical advantage of a block and tackle by counting the number of rope parts supporting the moving block • Relationship between load, mechanical advantage, and effort: ( P = \frac{W}{\text{mechanical advantage}} ) (ignoring friction) • The difference between ropes that actually support the moving block and the free (standing) end where you pull
• In figure G, how many separate rope segments are directly supporting the lower (moving) block that is attached to the 254 lb load? • Once you know that number, what mechanical advantage does that give you, and what does that do to the required effort P compared to the 254 lb load? • After you compute ( P = \frac{W}{\text{MA}} ), which of the answer choices is closest to that ideal value (assuming no friction)?
• Be sure you only count the rope segments that actually hold up the moving block, not every pass of the line you see in the sketch. • Confirm that you are using W = 254 lb for the load in your calculation. • Verify your final P is less than 254 lb and matches one of the multiple-choice answers before deciding.
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