Calculating Electric Field and Force in Vector Manipulation Problem

[Noreturn]

Homework Statement

1. Calculate the electric field at field point 3i + 6j created by a 5.50uC electric charge at 13i + 8j

2. Calculate the electric force on an electron at field point 3i + 6j and in the same electric field calculated
for the prior problem.

Homework Equations

The Attempt at a Solution

Going to combine 2&3 together to see how far I get

So I know I need to find the difference of the two so:

3-13= 10i
6-8= -2j

|r|=sqrt (10^2-2^2) =sqrt (104)

Then I have r^=10/sqrt(104)i+2/sqrt(104)j

Then that is where I get lost there like some many equations to choose from I do not know which one to use.

Cause electric field= force/charge.

So would it be r^/5.5uC?

 

[kuruman]

Then I have r^=10/sqrt(104)i+2/sqrt(104)j

You need a negative sign in front of the y-component. Also, it would help writing down all those equations that you have and are relevant. Then we could help you choose.

 

[Noreturn]

You need a negative sign in front of the y-component. Also, it would help writing down all those equations that you have and are relevant. Then we could help you choose.

Well it's just a test equation sheet it's a full page of equations. Here is some of the equations he gives us. Kinda hard to follow but they are there.
https://imgur.com/bnpPbng

 

[kuruman]

If you are about to take a test and this sheet was given to you to study from, it will be an excellent idea for you to know (a) what the symbols in these equations stand for and (b) when these equations are applicable. Here you want equations that are applicable to the electric field due to a point charge. Which one(s) do you think fit the bill?

 

[Noreturn]

Would it be E=Kq*r^?

So
E=(9*10^9)(5.5x10^-6/sqrt(104))(-10i-2j/sqrt(104)

E= -467i-93.3j

 

[kuruman]

Would it be E=Kq*r^?

No it would not. This equation is not even on the sheet you posted.

 

[Noreturn]

Which one is it suppose to be? I was following notes that we took in recitation and that was the final answer he came up with.

 

[kuruman]

The formula sheet that you were given shows equations that are starting points for solving problems. They are not final answers. If

... that was the final answer he came up with.

then that is an answer in the context of the problem that he solved, not necessarily something you can use for the problem you posted. You need to go back to the sheet and find the appropriate equation as I indicated in post #4. You have to learn how to do this on your own, else the equations sheet will be useless to you during a test.

 

[Noreturn]

So the only equation if I am looking right is:

E=Fon q/Q

So would it be (-10i-2j/sqrt(104))/(5.5*10^-6)

 

[kuruman]

That's the equation you should use to find the force in part 2. You still need to find the electric field at that point (part 1). Take a good look at all the equations on your sheet. You are probably on the brink of being frustrated, but you have to learn to be methodical.

 

[Noreturn]

That's the equation you should use to find the force in part 2. You still need to find the electric field at that point (part 1). Take a good look at all the equations on your sheet. You are probably on the brink of being frustrated, but you have to learn to be methodical.

Ok think I found it you actually have to combine a couple to get it to work. This is one in the book that looks more correct:

E=Kq/r^2(r^) - and then this would match the work we did in the recitation class :)

 

[kuruman]

That's the one. You already have $\hat{r}$ so go for it.