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If you just tie a rope around something and try to lift it, every inch that your hands move causes the load to move an inch as well, so you're lifting all of the weight. Throw that rope over a pulley and the situation doesn't change. You may be pulling down instead of up, but an inch of hand movement is still an inch of load movement, so a pulley by itself does NOT make work easier (unless its easier to pull down than up).

What you are thinking of is called a block and tackle. It is a little hard to describe without pictures, so I suggest going to Wikipedia. It makes work easier by allowing you to use less force over a longer period of time. Every extra loop of rope between the block and the tackle reduces the distance that the load is lifted when you pull on the end of the rope. With just one extra loop, when you pull the rope three inches, the load is only moved one inch. You might not think this is helpful because to lift 300 pounds 10 feet in the air, you'd have to pull the rope 30 feet, and it would take 3 times as long. The trick is, the total amount of work you're doing (300 pounds times 10 feet lifted = 3,000 foot-pounds) is always the same, so if the rope moves 30 feet, you only have to pull it with 100 pounds of force (100 pounds times 30 feet pulled = 3,000 foot-pounds). Use a block and tackle with four extra loops and you'll have to move the rope 90 feet to lift the load 10 feet, but it only takes around 34 pounds of force to do it.

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12y ago

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What is the formula for the percent efficiency of a pulley?

The formula for the percent efficiency of a pulley is (output work/input work) x 100%. It compares the output work (work done by the pulley) to the input work (work done on the pulley) to determine how efficient the pulley system is in transferring energy.


Do pulleys systems change how much work you do?

Pulley systems do not change the amount of work done; they only change the direction or magnitude of the force applied. In an ideal pulley system, the work input is equal to the work output, neglecting friction and other losses. The mechanical advantage gained from a pulley system allows the same amount of work to be done with less force or over a shorter distance.


A person does 50j of work to lift a crate using a pulley. the pulley's work output is 42j. What is the pully's mechanical efficiency?

The mechanical efficiency of the pulley is calculated as: (Work output / Work input) * 100%. In this case, it would be (42J / 50J) * 100% = 84%. The pulley is 84% efficient at converting input work into output work.


Ma of a pulley?

The mechanical advantage (MA) of a pulley system is calculated by counting the number of ropes supporting the moving block or load. For a single fixed pulley, the MA is 1 as it changes the direction of the force but does not provide any mechanical advantage. For a system with multiple pulleys, the MA is equal to the number of ropes supporting the load.


How is a flag a pulley?

A flag can be seen as a pulley when it is attached to a pole and raised or lowered by pulling on a rope. The pulley system allows for easy manipulation of the flag's position, similar to how a pulley facilitates the lifting of objects by distributing the force needed to raise them.

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