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What am I doing wrong?

  1. May 12, 2004 #1
    Alright, so I've got this volume problem and it seemed really easy, only my answer is off, if only by a little bit. The problem is this: There is a tunnel, with a cross-section in the shape of a parabola, that is 5 meters wide and 10 meters high (I got the equation to be y=-1.6x^2 + 10). It takes someone driving 50 miles per hour 3 minutes to get through the tunnel (2.5 miles or 4023.36 meters). What is the volume of the tunnel? Well, i took the integral of y=-1.6x^2 + 10 from -2.5 to 2.5 and got 100/3. then i multiplied that by 4023.36 and got 134112 cubic meters. But my teachre says this is wrong. I used a different conversion, where the 2.5 miles equalled 4022.857 meters, and she said this was closer. Am i just off with my integration, or am I just crazy?
     
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  3. May 12, 2004 #2

    HallsofIvy

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    I get 4022.5 m for the length of the tunnel. (One mile is 1.6091 km.)
     
  4. May 13, 2004 #3
    thanks! :)
     
  5. May 13, 2004 #4

    matt grime

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    I know SI units are slow to catch on in the US, and there's always the spelling issues, but it's "metres". Meters being something very different indeed, or have they decided to mix the spellings up?
     
    Last edited: May 13, 2004
  6. May 13, 2004 #5

    Zurtex

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    In England the SI measuring unit for distance is indeed spelt "metres".
     
  7. May 13, 2004 #6
    Americans use "meters," but not "metres."

    cookiemonster
     
  8. May 13, 2004 #7

    Njorl

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    In the US we spell "spelt" "spelled".
     
  9. May 14, 2004 #8
    Yes, that thing makes english a bit more difficut for people like me :)
     
  10. May 14, 2004 #9

    matt grime

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    both spelt and spelled are past tenses of spell, as mow can be mown or mowed depending on the case, but that's the problem of speaking a langauge that thinks it is latin when it is not.
     
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