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Homework Help: Particle moving in an electric field

  1. Nov 7, 2013 #1


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    1. The problem statement, all variables and given/known data

    A particle with charge q = 5.0 nC and mass m = 3.0 µg moves in a region where
    the magnetic field has components Bx= 2.0 mT, By=3.0 mT, and Bz= -4.0mT. At an instant when the speed of the particle is 5.0 km/s and the direction of its velocity is 120°relative to the magnetic field, what is the magnitude of the acceleration of the particle?

    ans: 38.86 m/s2

    2. Relevant equations

    I assume it is: Fm= qv χ B

    3. The attempt at a solution

    5*10-6(5*103) χ (0.02i + 0.03j - 0.04k)sin(120)

    this was my initial setup, but then I proceeded to do the following:

    5*10-6(5*103)sin(120)(.02) = c
    5*10-6(5*103)sin(120)(.03) = d
    5*10-6(5*103)sin(120)(-.04) = e


    and calculate the magnitude of the product --- then using this value in F=ma to determine the acceleration.
  2. jcsd
  3. Nov 7, 2013 #2
    This formula makes no sense. You have a number to the left of the cross, and a vector to the right.

    A cross product requires two vectors.
  4. Nov 7, 2013 #3


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    That's what i thought, which left be quite perplexed as to how i need to solve this. I wasn't sure what to do given that we were presented with a vector in the question.
  5. Nov 7, 2013 #4
    If you know the magnitudes of two vectors, and the angle between them, can you compute the cross product?

    What prevents you from doing this here?
  6. Nov 7, 2013 #5


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    I see where my error was, but my order of operations was not in the correct order. Thank you.
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