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Homework Help: Electric Fields

  1. Mar 6, 2005 #1
    1. An electron with a speed of 3.0 x 106 m/s moves into a uniform electric field of 1000 N/C. The field is parallel to the electron's motion. How far does the electron travel before it is brought to rest.

    I read the part of the text related to electric fields but I saw nothing that related it to the velocity of particle.

    2. An electron is released a short distance above earth's surface. A second electron directly below it exerts an electrostatic force on the first ele- just great enough to cancel the gravitational force on it. How far below the first electron is the second?

    Using Fg = G m1m2/r2 do I use this formula to find out the gravitational force and then set it equal to the electrical force? I'm a little confused on how to approach this.

  2. jcsd
  3. Mar 6, 2005 #2
    force acting on a charge in a field E is given by F= qE. Use newtons law to relate the acceleration with this

    you know v1, v2, a now find the time

    equate the gravitational force between earth and the electron with the coulomb attraction froce between teh electrons and solve for the r

    Hint the distance between the electron and the earth is not the same as the disatnce between the two electrons i guess the ygeave you radius of the earth didnt they?)
  4. Mar 6, 2005 #3
    No they didn't give me the radius of the earth. I gave you the entire problem.
  5. Mar 6, 2005 #4
    i guess they expect you to find it out

    the radius of the eaarth is 6.38 x 10^6 metres
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