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

by Ducati
Tags: grade, power, rating, watts or kwh
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Jan16-11, 07:08 PM
P: 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 !!
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Jan16-11, 09:43 PM
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kuruman's Avatar
P: 3,443
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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