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Electric potential and charge

  1. Jul 5, 2009 #1
    1. The problem statement, all variables and given/known data
    A point charge Q resides at the origin. A particle of mass 0.005 kg carries a charge of 2 µC. The particle is released from rest at x=3 m. Its kinetic energy as it passes x=0.5 m is 0.28 J. The Coulomb constance is 8.99x10^9 N*m^2/C^2. Find the charge Q. Answer in units of µC.


    2. Relevant equations
    Conservation of energy: PE_f + KE_f = PE_i + KE_i


    3. The attempt at a solution
    KE_i = 0 (starts from rest)
    PE_i = kqQ/xi = kqQ/3
    KE_f = .28 j
    PE_f = kqQ/.5
    kqQ[(1/.5) - (1/3)] = - .28
    (8.99 x 10^9)(2)Q[1.66667] = -.28
    Q = -9.3437152 x 10^-12 µC

    What am I missing or doing wrong?
     
  2. jcsd
  3. Jul 5, 2009 #2

    rl.bhat

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    Homework Helper

    (8.99 x 10^9)(2)Q[1.66667] = -.28
    Q = -9.3437152 x 10^-12 µC

    The given charge is 2μC
     
  4. Jul 5, 2009 #3
    Oh wow! Stupid mistake.
     
    Last edited: Jul 5, 2009
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