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Homework Help: Potential difference of falling charge particle

  1. Feb 15, 2009 #1
    1. The problem statement, all variables and given/known data
    A particle of mass 7*10e-5 kg and charge 1e-6 C from point A to point B a distance of 3 m in the earth's gravitational field. The kinetic energy of the particle decreases by 5.3mJ during this movement. The acceleration of gravity is 9.8 m/s^2. What is the potential difference Vb-Va?

    2. Relevant equations

    I don't know how to get the Electric Field. I know that its a positive charge going in the same direction as the gravitational field. Since the problem says that the final kinetic energy is decreasing, then I know the velocity is decreasing and giving me a hint that there is an electric field counteracting the gravitational field. I could use the sum of all forces to equate both the fields, but that is only when the charge would stop. Do I have the right Idea?

    3. The attempt at a solution

    Tried to do the sum of all forces and the conservation of energy.
  2. jcsd
  3. Feb 15, 2009 #2


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    W = q*ΔV

    So you have Δ½mv² and Δmgh.

    So if there was some work involved ... any ideas?
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