What Went Wrong with Calculating Pulley Efficiency?

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Homework Help Overview

The discussion revolves around a lab experiment involving pulleys, specifically focusing on the calculation of pulley efficiency based on measured forces and distances.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to calculate the efficiency of the pulley using the formula for work output and work input. They express confusion over the results, questioning whether the issue lies in their calculations or the experimental data.

Discussion Status

Participants are exploring the validity of the measurements taken during the lab. Some suggest that the measurements may not be accurate, leading to the discrepancies observed in the efficiency calculations. There is acknowledgment that the mathematical approach used by the original poster is correct, but concerns about the experimental setup remain unresolved.

Contextual Notes

Participants note that the measurements for applied force and distances were taken using a spring scale and a ruler, respectively. There is an implication that the accuracy of these measurements is in question, which may affect the overall results of the lab.

livvy07
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Homework Statement



we did a lab on pulleys. The weight lifted was 19.62 N. It rose 0.20 meter with us applying a lifting force of 11 N and pulling the rose a distance of 0.16.


The Attempt at a Solution


I tried to find the efficiency of the pulley, so E=work out/work in
so work out=FD=(19.62)(0.20)=3.92
and work in=FD=(11)(0.16)=1.76
yet the work output can't be greater than the work input, so I'm clearly doing something wrong.

Any ideas? Is it a math error or bad lab results? Any help would be great :)
 
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It's not a math problem. Those measurements don't make sense. How did you measure the applied force and distances?
 
oh no. That means the whole lab is wrong, but I'm doing the math right?
We measured the applied force with a spring scale and the distances with a ruler. i think the distances are completely wrong now...
 
livvy07 said:
That means the whole lab is wrong, but I'm doing the math right?
Yep, your math is fine. :frown:
 
oh well. Thanks for the help though! Guess I'll have to start making up numbers
 

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