A climber's gravitational potential energy increases from 14000J to 21000J while climbing a cliff. She expends 18000J of energy during this activity. What is the efficiency of this process?(adsbygoogle = window.adsbygoogle || []).push({});

A) 3%

B) 39%

C) 61%

D) 97%

Here is what I did.

Wpg = ∆Epg = Epg2-Epg1 = 21000-14000 = 7000J

% Eff = 100%(useful out)/total in = (100%)7000/18000 ≈ 39%

The answer key says it is 61% though. Is the answer key wrong or did I miss something?

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# Gravitational potential energy homework

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