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Homework Help: Heisnburg uncertainty

  1. Apr 24, 2009 #1
    1. The problem statement, all variables and given/known data
    A 1.70 kg block rests on the icy surface of a frozen pond, which you can assume to be frictionless. If the location of the block is measured to a precision of 0.30 cm, what is the minimum uncertainty in the block's speed, assuming the mass is known exactly?

    2. Relevant equations

    3. The attempt at a solution
    I plugged in all the values and got v. The answer was wrong. I then multiplies by .0003 and that was also wrong.
  2. jcsd
  3. Apr 24, 2009 #2
    potential sources of error # 1:
    0.3 cm = 0.003 meters, not 0.0003 meters

    potential source of error # 2
    they ask you for uncertainty in speed, while the equation for momentum p = mu considers VELOCITY
    an uncertainty in speed of 10m/s , for example, is equal to an uncertainty in velocity of 20 m/s, since a speed up to 10 m/s implies a range of velocities from -10m/s to +10m/s
    so try multiplying the speed by 2 :) (edit: or rather, try dividing the uncertainty in velocity you get by 2 to get the uncertainty in speed, since the block moves in both directions)
  4. Apr 24, 2009 #3
    1.03E-32 the velocity by 2 and got 5.16E-33 which is wrong by 10% to 100%.

    I used .003 meters.
  5. Apr 24, 2009 #4
    are you sure your math is right? using the version of the heisenberg uncertainty principle that you've provided (there are many variations of it) and the values for m and deltax youve given,
    i get an uncertainty in velocity of 3.24807255 × 10-32
    which is an uncertainty in speed of 1.62403627 × 10-32
  6. Apr 24, 2009 #5
    The math is right i did a million times. 1.62E-32 is wrong and it was last my chance. thanks, anways....
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