1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: Energy problem. Please help!

  1. Oct 6, 2007 #1
    How many joules of energy does a 100-watt light bulb use per hour?
    How fast would a 75 kg person have to run to have that amount of energy?
    Express your answer using two significant figures.

    I found the energy of the light bulb to be 3.6×10^5 J but I have no idea how to find the second part. Can someone please help me? thanks.
    Last edited: Oct 6, 2007
  2. jcsd
  3. Oct 6, 2007 #2
    The second question is not very clear. "How fast would a 75 <what?> person..."? Is that supposed to be kilograms?
  4. Oct 6, 2007 #3
    haha sorry! its supposed to be a 75kg person.
  5. Oct 6, 2007 #4
    Okay. So, any object in motion possesses kinetic energy, right?
  6. Oct 6, 2007 #5
    Yes. And K=1/2mv^2.
  7. Oct 6, 2007 #6
    Right...can you solve the problem now?
  8. Oct 6, 2007 #7
    so it would be 3.6×10^5 J=(1/2)75kg*v^2?
  9. Oct 6, 2007 #8
    got it!
    Thank you sooo much neutrino for pointing me in the right direction!! all i needed was a little help!
  10. Oct 6, 2007 #9
    You're welcome. :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook