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Homework Help: Impossible heisburg uncertainty question that makes no sense

  1. Apr 24, 2009 #1
    1. The problem statement, all variables and given/known data

    Suppose Fuzzy, a quantum-mechanical duck, lives in a world in which h = 2πJ · s. Fuzzy has a mass of 1.80 kg and is initially known to be within a pond 1.00 m wide. (a) What is the minimum uncertainty in the duck's speed?
    1(b) Assuming this uncertainty in speed to prevail for 5.40 s, determine the uncertainty in Fuzzy's position after this time.

    2. Relevant equations

    3. The attempt at a solution
    tried it a million different ways
  2. jcsd
  3. Apr 24, 2009 #2
    Well can you tell us what you tried, and tell us the right answer that you are failing to get?
  4. Apr 24, 2009 #3
    im doing online homework
  5. Apr 24, 2009 #4
    (a) I plugged all the numbers into the equation using 2pie for h and I get 8.88 and its off by orders of magnitude (b) I have no idea
  6. Apr 24, 2009 #5
    How did you get 8.88?
    if delta x * m * delta v = h/4 = 2pi / 4 = pi / 2
    delta v = Pi / (2 * 1 m * 1.8 kg) = Pi Js / 3.6kgm
    pi/3.6 is NOT 8.88 ... it's going to be a little less than 1

    and thats not even considering the fact that the uncertainty in speed should be half of the uncertainty of velocity (though ive even seen some textbooks that dont even consider the fact that velocity can be in both directions, and take the uncertainty in velocity to be the uncertainty in speed....however, the book that i learned quantum mechanics from had the uncertainty in speed as half the uncertainty in velocity for all the questions ....i dont know how your online service works, but if 8.88 is off by EXACTLY an order of magnitude, then the real answer would be 0.87 and not half of that)
    Last edited: Apr 24, 2009
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