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Homework Help: Find q for a moving particle

  1. Jan 29, 2013 #1
    1. The problem statement, all variables and given/known data
    A moving particle encounters an external electric field that decreases its kinetic energy from 8560 eV to 6770 eV as the particle moves from position A to position B. The electric potential at A is -50.5 V, and the electric potential at B is +25.9 V. Determine the charge of the particle. Include the algebraic sign (+ or −) with your answer.

    2. Relevant equations
    V=EPE/q, EPE=qEx=KE

    3. The attempt at a solution
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jan 29, 2013 #2


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    Staff: Mentor

    Hi Rae_4, Welcome to Physics Forums.

    Did you have a particular question about the problem? You seem to be on the right track with your attempt.
  4. Jan 29, 2013 #3
    Yeah. I'm trying that formula, but it keeps telling me my answer is incorrect. I'm not sure what I'm doing wrong. When I attempt the practice version it is trying to tell me the answer is times 10^-18 and nothing I have in that formula would give me a number that small. Are my formulas incorrect?
  5. Jan 29, 2013 #4


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    Science Advisor
    Homework Helper
    Gold Member

    The energy is given in eV. The charge of an electron is 1.6021765 × 10 −19 coulomb. That's pretty small.
  6. Jan 29, 2013 #5
    Figured it out. Thanks!
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