Which pulley setup needs the smallest force to lift the load?

Key takeaway: For pulley questions, the winning idea is usually mechanical advantage. More supporting rope segments means less force needed, although you often have to pull more rope.

I can’t see the three diagrams here, but the rule is straightforward:

• The pulley system with the greatest mechanical advantage needs the least force.
• In practice, that is usually the setup with the most rope segments supporting the weight.

So if Figure A, B, and C differ by the number of supporting strands, choose the one with the largest number of strands holding the 100 lb weight.

How to decide quickly

1. Count the rope sections lifting the load.
2. More sections = smaller input force.
3. Ignore the total rope length; the key is how the load is shared.

If one figure has a 30 cm pulley, another 10 cm, and another 15 cm, the size alone does not determine force as reliably as the rope arrangement does. The best answer is the figure with the highest mechanical advantage.

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Pitfalls the pros know 👇 A lot of students focus on pulley diameter or the amount of rope pulled. Those can affect distance moved, but the least force comes from the setup with the greatest support from the rope. Also, friction can spoil the ideal answer in real life, but most test problems ignore friction.

What if the problem changes? If two pulley systems have the same number of supporting strands, then they need about the same ideal force even if the pulley sizes differ. If friction is included, the smoother setup may require slightly less force than the one with more bending or rubbing.

Tags: mechanical advantage, supporting strands, ideal pulley system