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Power Equation?

  1. Oct 16, 2012 #1
    Power Equation??

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

    An ice cube is placed in a microwave oven. Suppose the oven delivers 135 W of power to the ice cube and that it takes 33200 Joules to melt it. How long does it take for the ice cube to melt?

    2. Relevant equations

    P = W / T

    3. The attempt at a solution

    Ok so I know the answer but this is confusing me... A unit of Power is J/second. So if we rearrange the equation and solve for T in minutes it would be.

    T = W / P,

    T = 135 / 33200 which doesn't give us the right equation to solve it...

    Instead it would be 33200 / 135 / 60 = 4.1 minutes, But why when I rearrange the equation doesn't it make sense?
    Last edited: Oct 16, 2012
  2. jcsd
  3. Oct 16, 2012 #2


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    Gold Member

    Re: Power Equation??

    33200 of what units? Badly stated question. "135 of power"?

    P = W/T ? What do you think P and W represent?
  4. Oct 16, 2012 #3
    Re: Power Equation??

    Power = Watts / Time, Fixed my typo up above.

    Ugh nvm I just went full retard. I read the question wrong. Ty anyway!
  5. Oct 16, 2012 #4


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    Gold Member

    Re: Power Equation??

    Use power = work (or energy) / time. Power has units of Watts.
  6. Oct 16, 2012 #5
    Re: Power Equation??

    Yea that's what confused me... I mixed up watts and work. Ty!
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