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Homework Help: What is the Efficiency of the system?

  1. Jul 26, 2014 #1

    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....
  2. jcsd
  3. Jul 27, 2014 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Looks like something wrong with the problem statement.
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