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Homework Help: Electrostatics question

  1. Nov 25, 2006 #1
    A uniform electric field has a magnitude of 3.0 103 N/C. In a vacuum, a proton begins with a speed of 2.4 104 m/s and moves in the direction of this field. Find the speed of the proton after it has moved a distance of 1.0 mm.

    I am confused with the fact that there is a velocity int his problem, I have not done electrostatics since last year and I do not recall any formulas with velocity or speed. I have used the equation [tex]E = F/q[/tex] to find Force...then I just don't know what to do after that, any suggestions or hints are appreciated, thank you!
  2. jcsd
  3. Nov 25, 2006 #2
    I don't know if its valid on such a small scale but you could try the following:

    You have the force. You know that F = ma. Once you find the acceleration, you could use a newtonian equation of motion. I believe there is one that relates acceleration, distance, initial and final velocity. The distance is given, and the initial velocity can be taken as 0.

    I think the equation is [itex]v_f^2 = v_0^2 + 2ad[/itex].
  4. Nov 25, 2006 #3
    Hm, I guess I could try that. you're right, but i am also not sure if it works on an atomic scale.
  5. Nov 26, 2006 #4


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    This is not a problem of force acting "on an atomic scale". It is a problem involving the motion of a small particle responding to an applied force moving a huge number of atomic diameters. The particle and it's motion may be analyzed using the laws of classical physics.
  6. Nov 26, 2006 #5
    Ah I see, so the Uniformly Accelerated Motion equations do indeed apply? I will try some calculations if you can check them for me I would greatly appreciate it.
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