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Homework Help: E-field of an ununiformly-charged rod

  1. Apr 5, 2006 #1
    ballistic particle and electric field

    Throughout space there is a uniform electric field in the -y direction of strength E = 450 N/C. There is no gravity. At t = 0, a particle with mass m = 5 g and charge q = -11 µC is at the origin moving with a velocity v0 = 35 m/s at an angle q = 25° above the x-axis.
    i found out that the magnitude of the force acting on the particle is 0.00495 N.
    the question is this: at t = 5 s, what are the x- and y-coordinatesof the position of the particle?
    x: 158.60 m, but i'm having trouble finding out what the y-coordinate would be, because of the electric field present in the -y direction.

    i tried this:
    the initial velocity in the y diction is 35 sin 25'.
    then, v_y = 35sin25 - at, where a = F/m. i've already found F, and m is given. so, a = 0.99
    then, v_y = 35sin25 - 0.99t. plug in t, i get 9.8416. but that's wrong.
    what am i doing wrong?

    Last edited: Apr 5, 2006
  2. jcsd
  3. Apr 5, 2006 #2


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    Homework Helper

    The integral is correct. How'd you get 7.2e10? K is of order e10 and A of the order e-6 so you should get something of the order e4.
  4. Apr 5, 2006 #3
    doh! i forgot that A is in µC.
    so... 2 * 9e9 * 4e-6 = 72000, and it's still wrong...
    the answer's supposed to be in N/C.


    oh. -72000. hehe.
    Last edited: Apr 5, 2006
  5. Apr 5, 2006 #4
    i'm recycling the thread. old post was edited to a new question.
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