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Difficulty: EasyPulleys and Pulley Systems

A military mechanic needs to lift an engine component that weighs 120 lbs120 \text{ lbs}. Match each pulley system configuration to the ideal effort force required to lift the component.

  • Single fixed pulley120 lbs120 \text{ lbs}
  • Single movable pulley60 lbs60 \text{ lbs}
  • Block and tackle with 4 supporting strands30 lbs30 \text{ lbs}

Answer

Single fixed pulley matches 120 lbs120 \text{ lbs}; Single movable pulley matches 60 lbs60 \text{ lbs}; Block and tackle with 4 supporting strands matches 30 lbs30 \text{ lbs}.
The effort force is calculated by dividing the 120 lb120 \text{ lb} load by the Ideal Mechanical Advantage (IMA) of each system: 1 for a single fixed pulley (120 lbs120 \text{ lbs}), 2 for a single movable pulley (60 lbs60 \text{ lbs}), and 4 for a 4-strand block and tackle (30 lbs30 \text{ lbs}).

Step-by-Step Solution

1
Determine the Ideal Mechanical Advantage (IMA) of the single fixed pulley.
IMA = 1.
A single fixed pulley only changes the direction of the force.
2
Calculate the effort force for the single fixed pulley.
120 lbs/1=120 lbs120 \text{ lbs} / 1 = 120 \text{ lbs}.
Effort = Load / IMA.
3
Determine the IMA of the single movable pulley.
IMA = 2.
A single movable pulley is supported by two rope sections, halving the required force.
4
Calculate the effort force for the single movable pulley.
120 lbs/2=60 lbs120 \text{ lbs} / 2 = 60 \text{ lbs}.
Effort = Load / IMA.
5
Determine the IMA of the block and tackle system with 4 supporting strands.
IMA = 4.
The number of supporting upward strands directly equals the IMA.
6
Calculate the effort force for the block and tackle system.
120 lbs/4=30 lbs120 \text{ lbs} / 4 = 30 \text{ lbs}.
Effort = Load / IMA.

Key Concept

The ideal effort force required to lift a load is the load divided by the Ideal Mechanical Advantage (IMA) of the pulley system.
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Topics

Pulleys and Pulley Systems

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