Can someone grade my practice test?

[MitsuShai]

1.
a) 0.102m
I set the electric fields equal to each other and canceled out the ks:
3q/(2d^2)= 8q/(d+x)^2 and then I solved from there.

b) 9.78*10^7
3q + 8q= 2.2e-5
E= 9e9 (2.2e-5/.045^2)= 9.78e7 N/C

c)1.56*10^-11
F=qE= 9.78e7*1.6e-19= 1.56e-11 N

2.A
3.D
4.D
5. I have no idea how to approach this problem.

Last Page: http://i324.photobucket.com/albums/k327/ProtoGirlEXE/lastpg.jpg

6.D
7. I have no idea. Wouldn't it be parallel to both the +x and -x axes?

 

[verty]

For problem 1, not enough work was shown and some errors were made early on. You get 5/30 on question 1.

 

[MitsuShai]

For problem 1, not enough work was shown and some errors were made early on. You get 5/30 on question 1.

where did I make an error?

3q/(2d)² = 8q/(d+x)²

sqrt(8q) 2d= sqrt(3q) d+x

.002449 d + .002449x = 3.6e-4

x= .10197 m

 

[verty]

The 5 marks were for part c because the method was correct.

 

[MitsuShai]

The 5 marks were for part c because the method was correct.

I don't see where I messed up at part a.

 

[MitsuShai]

nevermind, I got the answers for it.