# Homework Help: What is the Efficiency of the system?

1. Jul 26, 2014

### kathy

Question:

An hand crank is used to life a bucket of water from a well. The bucket and water have a combined mass of 12.0 kg and must be raised 8.5 m. The force used to lift this load is 40.0 N and must be applied over a total circular distance of 15.0 m. What is the efficiency of the system?

Related Equations:
W = (Force) (displacement)
W useful = (mass) (gravity) (height)
% Efficiency = useful work done / actual work done x 100%

Attempt at a Solution:

F = 40.0N
m = 12.0kg
h = 8.5m
g= 9.8N/kg
d= 15.0m
w= ?
w= (F)(d)
w= (40.0N) (15.0m)
w= 600J
w useful = ?
% Efficiency = ?
W useful = m g h
W useful = (12.0kg) (9.8N/kg) (8.5m)
W useful = 999.6J
w useful = 1000J
% Efficiency = useful work done / actual work done x 100%
% Efficiency = 1000J/600J x 100%
% Efficiency = 166%

The reason why I'm not sure I got the correct answer is because the efficiency of the system is over 100% instead of under....
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2. Jul 27, 2014

### CWatters

Looks like something wrong with the problem statement.