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Charged particle accelerates in an electric field?

  1. Feb 8, 2015 #1
    1. The problem statement, all variables and given/known data
    A positively charged particle initially at rest on the ground accelerates upward to 200m/s in 2.60s. The particle has a charge-to-mass ratio of 0.100 C/kg and the electric field in this region is constant and uniform.
    What are the magnitude and direction of the electric field?

    2. Relevant equations
    F=ma
    a=delta v/ delta t
    Electric Fields E=F/q
    Coulomb's Law F=kq/r^2 Not sure I need this one.

    3. The attempt at a solution
    E=F/q=ma/q=(m/q)a
    E=(10 kg/C)(200/2.6 m/s^2) = 769.23 N/C = 7.7*10^2 N/C Direction upward.

    Question seems pretty straightforward but it's telling me this answer is incorrect. If I have to incorporate Coulomb's law, I'm not sure how.
     
  2. jcsd
  3. Feb 8, 2015 #2
    Hint: Gravity ;)
     
  4. Feb 8, 2015 #3
    Thank you! Knew I was missing something obvious. Let me see if it works if I factor in gravity.
     
  5. Feb 8, 2015 #4
    ma = Fe - Fg
    ma = Eq - mg
    a = E(q/m)-g

    E = (a + g)/(q/m) = (76.923 + 9.81 m/s^2)/(0.100 C/kg) = 867.33 N/C = 8.7*10^2 N/C

    This look right?
     
  6. Feb 8, 2015 #5
    Yes, thats how i would solve it.
     
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