Climber efficiency calculation from gravitational potential energy change

[Erwin Schrodinger]

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?

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?

 

[Q_Goest]

I'd agree with your answer. They key must be wrong.