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Homework Help: Physics Midterm Help

  1. May 9, 2009 #1
    1. The problem statement, all variables and given/known data

    A two point charges (Qa and Qb) are placed along the y and x axis, as shown below:

    The Qa charge is placed 3 meters up from the y axis, which contains a -5.00 microcolumb charge. The Qb charge is placed 4 meters away from the x axis, which contains a 8.00 microcolumb charge.

    a. Calculate the net electric Field at the origin.

    2. Relevant equations

    E-Field on Qa = kq/r^2
    E-Field on Qb = kq/r^2

    [c]3. Attempt of a solution[/b]

    E-Field on Qa = kq/r^2 = (9.0 E9 N m^2/C^2)(-5.00 E-6 C)/(3m)^2 = -5000 N/m
    E-Field on Qb = kq/r^2 = (9.0 E9 N m^2C^2)(8.00 E-6 C)/(4m)^2 = 4500 N/m

    Where do I go from here? Do I add the E-Fields or Find the Pythagorean Theorem to find the magnitude of the E-Field?


    BTW...Dont worry Im not cheating...IM just asking a question that was asked on the midterm...that I didnt get the answer from.
  2. jcsd
  3. May 9, 2009 #2


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    Homework Helper

    The E-field is a vector field.

    So accounting for the contribution from the 2 charges means adding the vector components.

    Looks like Pythagoras would be the way to go to calculate |E|.
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