Electric Potential Produced by Point Charge

[deenuh20]

Homework Statement

A point charge of -8 µC is at the origin. What is the electric potential at
(a) (3.0m, 0),
(b) (-3.0m, 0), and
(c) (3.0m, -3.0m)?

Homework Equations

V=kq/r

The Attempt at a Solution

a & b) V=(8.99x10^9)(-8x10^-6)/3
V= -23973.3

c) V=(8.99x10^9(-8x10^-6)/6



I understand part a and b and got the correct answer. However, for part c, the only thing I am doing different is r=6 instead of 3 because the coordinates are (3.0m, -3.0m) and I am not getting the correct answer. I don't really understand. Thank you.

 

[Kurdt]

r does not equal 6. Think about the coordinate system.

 

[deenuh20]

I thought r=6 because there is 3 in the + x direction and 3 in the -x direction on either side of the origin (x=0) so I added them to get a total of 6 from -x to +x. I'm not really sure how to look at the coordinate system any other way?

 

[Kurdt]

The two numbers denote the x and y coordinates in a cartesian plane. How can you have a position with two x coordinates? Draw the x an y axes and work out what r should be for the (3, -3) point.

 

[deenuh20]

ohhhh wow I'm so blind. Thank you very much for your help!