# Homework Help: 4 questions regarding electric field

1. Jul 16, 2011

### realz

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

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2. Jul 16, 2011

### darkxponent

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

3. Jul 16, 2011

### darkxponent

and Q10 is same as Q9

4. Jul 16, 2011

### darkxponent

5. Jul 16, 2011

### realz

I dont get it. tried but it gave 3.53
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?

6. Jul 17, 2011

### cupid.callin

Dont just mug up the formula. its easier to find it by simple calculus

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.

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7. Jul 17, 2011

### darkxponent

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.