What is the electric potentional for these charges?

[Ammora]

Homework Statement

Find the electric potential energy for the following array of charges: charge q1 = +4.0 µC is located at (x, y) = (0.0, 0.0) m; charge q2 = +3.0 µC is located at (4.0, 3.0) m; and charge q3 = −1.0 µC is located at (0.0, 3.0) m.

_____ mJ

Homework Equations

U=kq1q2/r12
U=kq1q3/r13
U=kq2q3/r23

The Attempt at a Solution

Obviously, I just plug in the charges and the k constant, 8.99 x10^9, but I don't know what to put in for r. Do I have to calculate x and y components and add them up?

 

[Brown Arrow]

well i hope you know that each charge constrabute to potential. so say there are 1,2,3 charges. if you want to calculate the potential due to charge 1,2 on 3 just do 1 on 3 and 2 on 3. then add them up.

BA

 

[Ammora]

see "relevant equations". I already know I have to add them all up. I just don't know how to calculate r.

 

[Brown Arrow]

oh my mistake.

so we know x² + y²=r² <---Pythagorean theorem

from this and the corrdinate you are given you can find r

 

[Ammora]

I tried that, but it says it's wrong.

Using it, r12 would be: sqrt. (4^2 + 3^2) = 5

r13: sqrt. (0^2 + 3^2) = 3

r23: sqrt. (3^2 + 0^2) = 0

and plugging it into the equation kq1q2/r12, kq1q3/r13, kq2q3/r23 and adding them all up gives me 5.9 x 10^-4 Joules, which is 0.59 millijoules, which it says is wrong.

Can you please help me? I don't know what I'm doing wrong.

 

[Brown Arrow]

I tried that, but it says it's wrong.

Using it, r12 would be: sqrt. (4^2 + 3^2) = 5

r13: sqrt. (0^2 + 3^2) = 3

r23: sqrt. (3^2 + 0^2) = 0<---- this is wrong, it should be 3

and plugging it into the equation kq1q2/r12, kq1q3/r13, kq2q3/r23 and adding them all up gives me 5.9 x 10^-4 Joules, which is 0.59 millijoules, which it says is wrong.

Can you please help me? I don't know what I'm doing wrong.

btw can you post the original question. and is this from mastering physics?
...so are we trying to find the electric potential of q1 due to q2 and q3?.. because I am kinda confussed by the wording

 

[Ammora]

Find the electric potential energy for the following array of charges: charge q1 = +4.0 µC is located at (x, y) = (0.0, 0.0) m; charge q2 = +3.0 µC is located at (4.0, 3.0) m; and charge q3 = −1.0 µC is located at (0.0, 3.0) m.

We have to find the electric potential for all 3 charges.

 

[Ammora]

No, it's from Webassign, not a book.

 

[Brown Arrow]

first take the + and - into account
next say distance btw q1 and q2 take the differnece btw the point then use that to find distance...

oh mastering physics is like Webassign..

i used Webassign for math