# Converting (having major trouble)

BunDa4Th
I have a link to the image i am having trouble with it is D where i have to convert one SI unit, but really confuse how to do it.

http://img267.imageshack.us/img267/9623/webassignvy9.jpg [Broken]

any help or explanation on how do the conversion would be very helpful.

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Staff Emeritus
Gold Member
Okay, I'll get you started. From your responses to the quiz, it is clear that you realize that:

1 W = 1 J/s

Therefore, 1 J = 1 W*s

A joule of energy is the amount of energy expended after one second by something that uses one watt of power.

Therefore

1 kWh = ??? W*s

well, how many watts in a kilowatt? How many seconds in an hour? It's really as simple as that!

BunDa4Th
1 kWh = (10^3 W)(3600 sec.) = 3600000 W*s

BTW, its not a quiz it's homework given to us to review for the quiz/test.

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Staff Emeritus
Gold Member
Ok, hw. Cool...

So your answer looks right to me. In which case, if I'm reading your homework right, the cost is 7 cents per 3 600 000 joules = whatever

Let me know if that gives you the right answer!

BunDa4Th
7 cent is incorrect which i have tried earlier.

Staff Emeritus
Gold Member
No no no! It's 7 cents for every kWh = 3600000 J. They want to know what it is on a PER JOULE basis. Now that you have the number of joules in a kWh, you can easily calculate the unit price PER JOULE.

the cost is 7 cents per 3 600 000 joules = whatever

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