Posted by **Andrea** on Wednesday, October 17, 2007 at 4:54pm.

If your last electric bill for sept. was $105. If the average price is 6.5 cents per kw, how many kw did your household use in September?

1kw/.065 = x/$105

.065x=105

x=1615.38 kw

is this correct?

How many Joules is that?

I know that 1W =1Joule/second

1kw=1000W

so 1615.38kw /1000 =1.61538 W

then I get 1.61538W

but how would i get this into joules?

- Physics -
**bobpursley**, Wednesday, October 17, 2007 at 5:24pm
the question is really flawed if you typed it correctly. One pays for energy, not power. The price on an electric bill is for kw-hrs (energy), not per kilowatt.

I don't know what to make of the question at all, especially the second part. Kwatts are not equivalent to joules unless you have time enter into the equation.

- Physics -
**drwls**, Wednesday, October 17, 2007 at 5:26pm
You either copied something wrong, omitted an "h" when typing, or your teacher needs a science refresher course. ENERGY is measured in kilowatt-hours (kwh) not kilowatts (kw). POWER is measured in kilowatts. What you pay for is energy, per kwh. Energy is power times time.

Total bill = (no. of kwh) x (cost per kwh, in dollars)

105.00 = N x 0.065

Your answer is numerically correct, but the units are wrong.

To convert kwh to Joules, multiply the number of kwh by this factor:

(3600 Joules/watt-hour)x(1000 watt/kw)

The 3600 comes from the number of seconds in one hour. 1 Joule = 1 Watt-sec

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