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Homework Help: Physics Lab - Mechanical equivalent of heat

  1. Apr 13, 2009 #1
    1.) Using the table provided what is the change in thermistor resistance if temperature rises from 21 C to 30C?

    The ohm values for resistance are 120810 for 21C and 79,422 for 30C. I just subtracted the two numbers and got -41,388 ohm. I hope that's right!!

    2.) This lab involves a spool that has a crank on it and also has a string wrapped around it several times with a mass hanging on the edge of the string hanging vertically.

    The question asks: Does it matter how many turns of cord surround the spool? Why? I said it does matter because the length of cord wrapped around determines the amount of friction. Is that right?

    3.) Does it matter how fast you turn the crank? Why?
    I put it does matter because the faster you crank the more revolutions and therefore gets more work done per turn. If turned quickly enough it can make the cord tension vanish. Is there anything I'm missing in this explanation?

    4.)Suppose, the cord where it is attached to the post, is under tension during the experiment. Would this lead to error in your measured value of the mechanical equivalent of heat? If so, would you value be too large or too small?

    I would say the measured value would affect the heat but I don't know how to explain this. Please help! Thanks!!! Guys!
  2. jcsd
  3. Apr 13, 2009 #2
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