Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Power problem!

  1. Dec 3, 2007 #1
    [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=[tex]\frac{w}{t}[/tex] --> 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 [tex]10^{5}[/tex].

    (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.

    Please help, we didn't get any notes to refer to for this homework and it is our first day learning about Power. :confused:
    Thanks so much.:smile:
    Last edited: Dec 3, 2007
  2. jcsd
  3. Dec 3, 2007 #2


    User Avatar
    Homework Helper

    For part (a): since 1 Watt = 1 Joule/second, you need to change the 10 minutes into seconds to keep your units consistent.
  4. Dec 3, 2007 #3
    ok thanks...i got part a! now im just workin on b...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook