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Force of 2 Point Charges

  1. I've been working on the following problem but when I try my answer online, it keeps coming up as incorrect. A charge Q1=-9.4 C is 4.8 m from a charge Q2 = 3.6 C. What is the magnitude of the electrostatic force on Q1?

    I'm pretty sure for this its just Coulomb's Law so:
    F = (k(Q1*Q2))/r^2
    F = ((8.9876*10^9)(-9.4*3.6))(4.8^2)
    F ~ 1.32 * 10^10 N
    Taking into account sig. figs, my final answer is 1.3*10^10 N. \

    However, this keeps coming up as incorrect. Am I overlooking something? Thanks in advance for the help!
     
  2. jcsd
  3. nrqed

    nrqed 3,048
    Science Advisor
    Homework Helper

    Sounds right to me. Are you sure that the charges are given in Coulombs (and not microcoulombs or nanocoulombs)? Other than that, I can't see anything wrong.

    Patrick
     
  4. Yep, I just looked it over again and all charges are given in Coulomb's. I think I might email my professor to see if he can look it over. Perhaps its a bug in the online grading system? I'm fairly confident in my answer. Thanks for looking it over!
     
  5. nrqed

    nrqed 3,048
    Science Advisor
    Homework Helper

    You are welcome. Yes, it might be a big. Or maybe the system is expecting an answer with 3 sig figs (even though the answer should really have only two sig figs). But your answer is correct.

    Best luck!

    Patrick
     
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