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Units in a heat transferred calculation

  1. Mar 11, 2012 #1
    I'm trying to do a calculation using: Heat transferred = mass x specific heat capacity x change in temperature
    q=mc∆T

    But the value I'm trying to calculate is the change in temperature so I've rearranged the equation to ∆T= q/mc

    I think the numbers and answer I have are correct, but the units are confusing me. My answer clearly needs to be in °C, the joules on the top and the bottom will cancel out but then on the bottom I'm left with kg multiplied by kg-1.

    3.54 J
    450 kg x 4.2 x 103 J kg-1 °C-1

    As far as I know, these don't cancel eachother out so my answer has the wrong units. I don't know if I've done the entire thing wrong if I'm just confusing myself over something silly. I'd appreciate any help at all.
     
  2. jcsd
  3. Mar 11, 2012 #2

    Redbelly98

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    So are you wondering what to do with kg·kg-1?

    kg is the same as kg+1, so what you really have is kg+1·kg-1. Simplify that using algebra rules for exponents, and you should be all set.
     
  4. Mar 11, 2012 #3
    ohh I feel really stupid now. Any number to the zero power is equal to 1. I already knew this but mistakingly thought that the result of calculating kg0 would be 1kg, but the answer is literally just 1, isn't it? So the kg does actually cancel. I feel silly for not realising, thanks very much for the help!
     
  5. Mar 11, 2012 #4

    Redbelly98

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    You're welcome, glad it worked out for you.
     
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