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Grade 9 Power Problems (Watts/kWh, power rating question)

  1. Jan 16, 2011 #1
    1. The problem statement, all variables and given/known data

    So, i need to learn how to do questions with finding out the power rating, and energy etc etc from using the triangles given and i am having some trouble since some of my triangles are missing and i need some help with converting.

    2. Relevant equations

    1) A hot plate has a power rating of 1250 Watts. How much energy in Kilowatt-hours is used when this hot plate is used for 3.00 hours at a banquet?

    3. The attempt at a solution

    I converted the watts to kWh so i turned 1250 to 1.25. On the triangle with the variables of "P," "E," and "T," it says E=Pt So i did 1.25*3 and got 3.75kWh.
    The problem is that i thought that "E" was always in joules or Kilojoules so i do not think the answer can be 3.75kWh since that is the power rating.
    If i am correct, i need help with converting the 3.75kWh into joules if that is what i need to do.

    Thanks !!
  2. jcsd
  3. Jan 16, 2011 #2


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    Homework Helper
    Gold Member

    1 Watt = 1 Joule/second
    1 Watt*hour = (1 Joule/second)*3600 seconds = 3600 Joules
    1 kWh = 1000 Watt*hour

    Got it?
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