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Homework Help: Uncertainties in the momentum and kinetic energy of the proton?

  1. Apr 7, 2010 #1
    1. The problem statement, all variables and given/known data
    A proton in a tin nucleus is known to lie within a sphere whose diameter is about 2.2 multiplied by 10E-14 m. What are the uncertainties in the momentum and kinetic energy of the proton?

    2. Relevant equations
    delta(x)*delta(p) >= hbar
    delta(E)*delta(t) >= hbar

    3. The attempt at a solution

    I understand the first part finding the uncertainty of the momentum, which is simply. . .

    1.05E-34 J(s) / (2.2E-14 m) = 4.77E-21 kg(m/s)

    I don't however, in any way understand finding the uncertainty in the kinetic energy. . . Howe are we suppose to know this if we aren't told the time (or does that matter). I know the answer should be something times E-14, but I would like to know how to modify and manipulate this equation (delta(E)*delta(t) >= hbar.

    Any help would be appreciated.
  2. jcsd
  3. Apr 8, 2010 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    I think you just need to find the kinetic energy corresponding to the momentum you have calculated.
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