Conservation of energy/ efficiency question.

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Homework Help Overview

The problem involves a climber's change in gravitational potential energy while climbing a cliff and the energy expended during this activity. The subject area relates to the concepts of conservation of energy and efficiency calculations.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the definition of useful output and total input energy, with some questioning how to identify these values in the context of the problem. There is also confusion regarding the calculation of efficiency based on different interpretations of the energy values provided.

Discussion Status

Participants are actively engaging with the problem, exploring different interpretations of the energy values and discussing the efficiency calculation. Some have noted discrepancies between their calculations and the expected answer, leading to further questioning of the provided information.

Contextual Notes

There is mention of an exam review booklet that provides a different answer than what some participants found online, indicating potential discrepancies in the source material being referenced.

maccha
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Homework Statement



A climber's gravitational potential energy increases from 14000 J to 21 000 J while climbing a cliff. She expends 18 000 J of energy during this activity. What is the efficiency of this process?


Homework Equations



Efficiency= useful output/ total input

Total energy before = total energy after

The Attempt at a Solution



Well, I've been able to solve all other efficiency/ conservatino of energy questions but for some reason I just don't understand this one. I don't understand what to consider as the input or the useful output energy. Thanks for your help!
 
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What was her change in potential energy? Isn't that the useful output?

The work gone into increasing potential energy?
 
Okay well then useful output would be 7 000 J / 14 000 J (input), and efficiency would be 50 % ? But the answer says it is 61 %.
 
No. She expended 18,000 J not 14,000.
 
Oh! Okay. Still doesn't work with the answer though ah.
 
maccha said:
Oh! Okay. Still doesn't work with the answer though ah.

It is 1 - the answer.

I think the answer may be wrong?
 
Yeah we have an exam review booklet which said that was the answer, but I just found the same exam on the internet and it said yours was right, so the booklet answer was wrong. Thanks!
 
That's a relief. Wouldn't make sense otherwise.

Good luck.
 

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