1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Electrical forces and energy: Electric Potential help

  1. Mar 15, 2013 #1
    1. The problem statement, all variables and given/known data
    Hi, I have a couple different problems that I did not understand.
    I have the images here.
    The problems which I did not understand were: 12, 13, 17. [EDIT: I calculated answer to 12 using conservation of energy.]
    For 13, I know how the graph looks; however, I'm not sure how to calculate the two zeros as well as the local minimum on the left.



    2. Relevant equations


    3. The attempt at a solution

    12. No idea whatsoever. I tried using the electrostatic forces equation, however there is no specific "r" value between where the Q2 and the other Q's are, so you can't do that. I think it might have something to do with momentum, but I'm not sure how to apply that.

    EDIT: Uo + Ko = Uf + Kf. Using this, I got the right answer Vo = 6.19 m/s.

    13. I already have the graph which looks like this:


    The black spots are the values I need to find. I tried using the field graph to find the values, but it failed. I also tried using kq/r = kq/r to find the zeros, but I didn't get the right answers again.

    17. This one I know how to do, I'm just confused on what to plug in.

    The ΔV = -EΔx, so then you do Delta V (125 > 100) + Delta V (100 > 50) + Delta V (50>25) and that should be the answer. However I'm not sure what to plug in for the "q" in each case.

    12. 6.19 m/s
    13. The values of the two zeros are -5.46 m and 1.0 m. The y-value of the local min is -2.00 m.
    17. 3.42 * 10^4 V

    I'd appreciate it for any help. Thank you!
    Last edited: Mar 15, 2013
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted