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Calculating Power of a Light Bulb

  1. Dec 8, 2008 #1
    1. The problem statement, all variables and given/known data
    How many Joules of energy does a 100 watt light bulb use per hour? How fast would a 70-kg person have to run to have that same amount of kinetic energy?

    2. Relevant equations
    How fast would a 70-kg person have to run to have the same amount of kinetic energy?

    3. The attempt at a solution

    1 watt = 1 J/S so... 100 J/S * 3600s = 360,000 J

    360,000 kg m^2/s^2 ÷ 70 = 5142.86 m^2/s^2

    my only question would be do you just square root the value and would it remove both ^2?
  2. jcsd
  3. Dec 8, 2008 #2


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    Yes a sqrt() acts on the units as well as the number
    I think you are missing a factor 2 somewhere, ke = 1/2 m v^2
  4. Dec 8, 2008 #3
    ok thanks for your help, i'm pretty sure i can handle it from here.
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