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Homework Help: Lorentz Force Law, am i messing up vector algebra?

  1. Nov 6, 2005 #1
    Okay here is my work:
    and here is my calculations part:
    http://img136.imageshack.us/img136/5539/lastscan7qc.jpg [Broken]
    Problem says:
    14. [HRW7 28.P.008.] An electron has an initial velocity of (14.0 j + 21.0 k) km/s and a constant acceleration of (3.50 10^12 m/s2) i in a region in which uniform electric and magnetic fields are present. If B = (400 ┬ÁT) i, find the electric field E.
    V/m i + V/m j + V/m k

    I know i'm getting the wrong answer because i tried to submit the i component and it was wrong i got:

    any ideas where i screwed up?
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Nov 6, 2005 #2
    I haven't really done the question here, but from the looks of it you have rounded your values incorrectly. Are you using the full calculator value in your calculation though? If so then it doesn't matter, but if you're using rounded values then your answer might just be out by a little. You're using SI units throughout so you definitely have V/m as your final unit.
  4. Nov 6, 2005 #3


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    Homework Helper

    last time I checked, electrons had charge negative (-) e !
  5. Nov 7, 2005 #4
    so u don't use the magntiude of the charge in that equation?
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