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Homework Help: Challenging Question

  1. Feb 6, 2007 #1
    1. The problem statement, all variables and given/known data

    An electron is fired at a speed vo = 5.0 106 m/s and at an angle o = -44° between two parallel conducting plates that are D = 3.7 mm apart, as in Figure P16.66. The voltage difference between the plates is V = 100 V.

    (a) Determine how close, d, the electron will get to the bottom plate.

    2. Relevant equations

    Conservation of energy:
    (1/2)mv^2 = -qEd

    3. The attempt at a solution

    I was thinking conservation of energy because the electron is initially moving and when it reaches max, it stops and KE is converted to PE.
    (1/2)(9.109e-31)[(5e6)sin(44)]^2 = (-1.602e-19)(27027.02)(d)
    d = 0.001269 m

    E = (100/0.0037) = 27027.2 N/C

    Anyone knows what is wrong?

    Attached Files:

    Last edited: Feb 6, 2007
  2. jcsd
  3. Feb 6, 2007 #2
    I would probably tackle it with forces so that the vectors remain intact. You never said what the question was asking for.
  4. Feb 6, 2007 #3
    sry forgot the question. I edited the post. I was thinking of using projectile motion to solve this question, but I can't solve for the force that moves the electron towards the positive plate.
    I know F = qE

    edit: omg I just told myself how to solve this. Nevermind, I think I know how to do this. :]
    Last edited: Feb 6, 2007
  5. Jul 19, 2007 #4

    is that the correct method? i tried using it and got an incorrect answer
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