If a block and tackle arrangement were rigged as illustrated in figure "D", the amount of force "P" required to hold the 283 pound load stationary would be __________. See illustration GS-0110.
• Mechanical advantage (MA) of a block and tackle = number of rope parts supporting the moving block (ignoring friction). • In equilibrium, sum of upward forces = weight of the load (283 lbs). • Each rope segment in the system carries the same tension P if the pulleys are ideal.
• Trace the rope in figure D carefully and count how many rope segments are directly lifting the moving block and load. • Once you know that number, set up the balance: (number of supporting parts) × P = 283 lbs, then solve for P. • After you get the ideal P, compare it with the choices and think about whether the exam expects you to ignore friction or allow for a small loss in efficiency.
• Be sure you only count rope segments that actually pull up on the moving block/load, not the free end you pull on if it is not attached to the block. • Check that your calculated P is in the same range as the answer choices; if not, re‑trace the rope path in figure D and recount the supporting parts. • Verify your final selection by quickly multiplying your chosen P by the number of supporting parts to see if you get approximately 283 lbs.
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