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Homework Help: Physics Electrical Forces

  1. Apr 24, 2005 #1
    I have some more questions from a physics worksheet, this time on electrical forces. here are the questions and the answers i got, thanks in advance!

    http://i2.photobucket.com/albums/y15/seiferseph/electircalforces.jpg [Broken]


    1) Fe = kQq/R^2, i get 3.6 x 10^10 N
    2) a) Fg = GMm/R^2, i get 7.80 x 10^-47 N
    b) Fe = kQq/R^2, using 1.6x10^-19 for both Q and -1.6x10^-19 for q, i get Fe = -8.86x10^-8 N
    3) Q = n*e, Q/e = n. n = 2.5x10^19. i have a question though, can it be negative? (the charge is negative)
    4) How do i do this one? is it just a simple ratio problem?
    5) a) i calculated the force of each one seperately, i used 2*1.6x10^-19 for the charge of the middle one, because it has two protons.
    F 1 on middle = k*q1*qmiddle/R^2 = 3.2x10-16
    F 2 on middle = k*q2*qmiddle/R^2 = 1.44x10-15
    and i get 1.76x10^15 N to the right
    b) F = m*a, F/m = a, where m is 4*1.67x10^-27 = 2.6x10^11 m/s^2

    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Apr 24, 2005 #2


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    1) 2) Correct approach.. did not check your computations
    3) The negative charge comes from negatively charged electrons. The NUMBER of electrons is positive.

    4) Yes. You can find the charge to mass ratio for one electron.

    5) a) Are these forces in opposite directions?
    b) There is no b showing
    Last edited by a moderator: May 2, 2017
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