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4 questions regarding electric field

  1. Jul 16, 2011 #1
    1. The problem statement, all variables and given/known data

    Questions attached

    2. Relevant equations

    K=9X10*9
    E=KQ/R*2
    vf=vi+at

    3. The attempt at a solution

    I only have idea on question 14 but it's wrong. For others I don't , I can only do simple one like if all the charge in x axis

    Question 14:
    qE=ma
    qE/m=a = 20
    vf=vi+at
    =50+20(2)
    =90

    *I've been told that all of the answers for the questions is A
     

    Attached Files:

  2. jcsd
  3. Jul 16, 2011 #2
    for Q9 we can use formulae for Electric Field at centre of a circular arc

    E = (kq/r) * r*(sin(alpha))/alpha

    where alpha is half the angle of arc. In this case alpha= 45
     
  4. Jul 16, 2011 #3
    and Q10 is same as Q9
     
  5. Jul 16, 2011 #4
    answer of Q12 :A
     
  6. Jul 16, 2011 #5
    I dont get it. tried but it gave 3.53
    can you upload worksheet
    I can do if the point of charge is in y but now if it's in 2 side x and y, can you show me the way?

    what about question 14?
     
  7. Jul 17, 2011 #6
    Dont just mug up the formula. its easier to find it by simple calculus

    attachment.php?attachmentid=37243&stc=1&d=1310885847.png

    consider two element dx at angle θ from central element.
    their field's sin components will cancell out and thus only cos will remain.
    now just integrate.
     

    Attached Files:

  8. Jul 17, 2011 #7
    i just uploaded it but they removed it because i solved the whole question. We cant provide whole solution as per rules of PF. I just read all the rules. And i am not going to break more rules because i already have recieved a warning. We can only help you solve it.

    You should also read the rules https://www.physicsforums.com/showthread.php?t=414380 as you also new to this website.
     
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