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Thermal elongation-2

  1. Sep 15, 2014 #1
    1. The problem statement, all variables and given/known data
    A steel ruler is correct at 180c. when the temperature was 350c a distance of 28.85 m was measured between 2 points. what is the correct distance

    2. Relevant equations
    $$L=L_0(1-\alpha \Delta t)$$

    3. The attempt at a solution
    $$1+12E-6 \cdot 17^0=1.000204$$
    How many big units enter in the original, correct, x, length:
    $$\frac{x}{1.000204}=28.856$$
    Is it correct?
     
  2. jcsd
  3. Sep 15, 2014 #2
    "A steel ruler is correct at 180c. when the temperature was 350c a distance of 28.85 m was measured between 2 points. what is the correct distance"

    LOGIC TEST :biggrin:! Does steel expand or contract when it gets hotter? Should your answer be larger or smaller than the distance given?

    I suggest making 28.85 your original length.

    Edit: clarity
     
    Last edited: Sep 15, 2014
  4. Sep 15, 2014 #3
    Of course at a lower temperature the distances on the ruler shrink, so the count is higher, that's my logic.
    The measure is taken at 35c, so at 18c the length will be longer, on the ruler, my formula is correct, i am pretty sure
     
  5. Sep 15, 2014 #4
    Oh, forget what I said about the formula thing, I did it two different ways and ended up countering what I said with "making 28.85 the original length".

    Anyways at a lower temperature the distance shrinks. So the count is higher? I think you are confusing the question a bit. You're not actually using to ruler to measure itself. Lets say the ruler is at 35C, and you grab another ruler to measure the distance between two points on the ruler, lets say from the 5cm to 20cm mark. When the temperature is 18C, you are still measuring from the 5cm to 20cm mark, but as you just said, the ruler shrunk, therefore your value should be smaller, at least this is how I interpreted the question, I see how you see the question.

    Edit: The main difference I can tell between our approach is when it says the distance between 2 points, I assume the 2 points are on the ruler. In your case you say the points are not on the ruler, in which you would be correct. but I don't know which scenario the question wants, my reading comprehension sucks.
     
    Last edited: Sep 15, 2014
  6. Sep 15, 2014 #5
    The points are outside the ruler
     
  7. Sep 15, 2014 #6
    then its right srry for confusion
     
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