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Need help with unit conversions!

  1. Jul 17, 2009 #1
    1. The problem statement, all variables and given/known data
    A steam iron draws 5.3 A from a 114 V line. (a) How much internal energy is produced in 76 minutes? Answer in J. (b) How much does it cost at $0.75/kW*hr to run the steam iron for 76 minutes? Answer in units of cents.

    2. Relevant equations
    1) U = VIt

    3. The attempt at a solution
    Using equation 1, I found the internal energy produced to be 2755152 J. However, I'm having a problem with figuring out part (b). I know I'm supposed to convert J to kW*hr in order to figure out the cost and that 1 watt = 1 J/s. Using that information I divided the internal energy by the time, 4560 seconds, giving me 604.2 watts or 0.6042 kW. I then times that by the cost per kW/hr and the amount of time in hours. I got 0.57399, but for some reason it's not the right answer.
  2. jcsd
  3. Jul 17, 2009 #2


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    2755152 J =2755152 Ws

    Divide by 1000 to get it in kWs, then divide by 3600s to get it in kW*hr
  4. Jul 17, 2009 #3


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    Maybe enter it in cents?
  5. Jul 17, 2009 #4
    I tried that and I get the same exact answer that I got. I even tried putting it in as 0.57 but that was marked wrong as well...
  6. Jul 17, 2009 #5


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    Your answer is $0.57399, convert that into cents.
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