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Help rearranging a formula to solve for different variables

  1. Sep 21, 2016 #1
    1. The problem statement, all variables and given/known data
    I just got this formula from class : Q=mc(T2-T1) and got task to make 2 more formulas from this one


    2. Relevant equations
    How do I make these formulas : T1=? and T2=?



    3. The attempt at a solution
    T2=Q:mc-T1
    T1=-T1
    T1=Q:mc+T2



    Thanks for help
     
  2. jcsd
  3. Sep 21, 2016 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF.

    The equations look okay (see kuruman's post below) except for the bolded part. What do you mean by that equation?
     
    Last edited: Sep 21, 2016
  4. Sep 21, 2016 #3

    gneill

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    Note that I changed the thread title to: "Help rearranging a formula to solve for different variables".

    I think this will make it a bit more clear what the thread is about.
     
  5. Sep 21, 2016 #4

    kuruman

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    This equation is also problematic. Starting with your equation Q=mc(T2-T1), it looks like you first divided both sides by mc. That is good. What expression did you get? And once you got that expression, what did you do to it to get T2=Q:mc-T1 ?
     
  6. Sep 22, 2016 #5
    I got Delta T=Q:mc

    Delta T=T2-T1 so formula is T2-T1=Q:mc and I just used simple math trick that if you change sides, it just changes from + to - and - to + e.g x=+4 meaning x-4=0

    So from T2-T1=Q:mc formula I got these two:
    T1=Q:mc-T2
    T2=Q:mc+T1
     
  7. Sep 22, 2016 #6

    kuruman

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    You got the equation for T2 correct this time, but the equation for T1 is incorrect. Starting with T2-T1=Q:mc what do you get, using your simple math trick, when you move T1 to the left side and Q:mc to the right side?
     
  8. Sep 22, 2016 #7
    T2-T1=Q:mc
    T2=Q:mc+T1
    T2:Q*mc=T1
    T1=T2:Q*mc
    Did I get it right this time?
     
  9. Sep 22, 2016 #8

    kuruman

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    Sorry, no.

    T2=Q:mc+T1 is correct. You want to have Q:mc on the other side. What does your simple math trick say you should do to achieve this goal? You said it yourself
    So ...
     
  10. Sep 22, 2016 #9
    T2-T1=Q:mc

    I can't just move Q:mc freely becouse of division between Q and mc and because of multiplication between m and c.
    E.g ρ=m:V
    Makes m=ρV
    So I can't use my math trick
    Sorry if I got your question wrong
     
  11. Sep 22, 2016 #10

    kuruman

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    Yes you can. Here is how and why. Let w = Q:mc. Then your equation becomes T2-T1 = w. Now move things around to get T1 alone on one side. Finally, replace w with what it is the same as, namely Q:mc. This is how algebra works!
     
  12. Sep 22, 2016 #11
    +T2-T1=+w
    +T2=+T1+w
    +T2-w=+T1
    T2-Q:mc=T1
    I hope i got it right this time, did I?
     
  13. Sep 22, 2016 #12

    kuruman

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    You did, and I hope you learned something from this experience. :smile:
     
  14. Sep 22, 2016 #13
    Thanks for your help. I definitely learned a lot.
     
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