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Homework Help: Webassign due in like half hour! i have the problem down but its not working

  1. Mar 17, 2008 #1
    webassign due in like half hour! i have the problem down...but its not working!!!

    1. The problem statement, all variables and given/known data

    A steam iron draws 8.0 A when connected to a potential difference of 120 V.
    (a) What is the power rating of this iron? 960 W <<<<correct

    (b) How many joules of energy are produced in 20.0 min?
    320 J <<<incorrect why???

    (c) How much does it cost to run the iron for 20.0 min at $0.010/kW·h?
    .0032 $ <<<<correct

    2. Relevant equations

    for part b: 960*(20/60) = 320

    whys it wrong?!
    Last edited: Mar 17, 2008
  2. jcsd
  3. Mar 18, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    One Watt = one Joule per second. You need to multiply the power (960 W) by the time in seconds (not hours).
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