# Power problem!

1. Dec 3, 2007

### aquamarine08

[SOLVED] Power problem!

1. The problem statement, all variables and given/known data

(a) How many joules of electrical energy are used by a 1650-W hair dryer in 10 min? (b) If the dryer is operated a total of 4.5 h during one month, how much will this contribute to the electrical bill if the billing rate is 12 cents/kWh?

2. Relevant equations

P=$$\frac{w}{t}$$ --> w=Pt

3. The attempt at a solution

(a) w=Pt -> (1650)(10)= 16500 J

I figured since the answer was supposed to be in Joules, I would use the equation w=Pt to figure out the amount but I ended up getting the wrong answer. The correct answer is 9.9 x $$10^{5}$$.

(b) Since I didn't get the right answer for (a) I knew my answer wouldn't be right here either. I don't really know how to solve this question either but I figured I should convert the 4.5 h into minutes so it matches the amount for part (a)..so I got 190 minutes, and that's pretty much it.

Thanks so much.

Last edited: Dec 3, 2007
2. Dec 3, 2007

### hage567

For part (a): since 1 Watt = 1 Joule/second, you need to change the 10 minutes into seconds to keep your units consistent.

3. Dec 3, 2007

### aquamarine08

ok thanks...i got part a! now im just workin on b...