Vectors are confusing me. I'm not sure if I'm doing it right

[josh12399]

Homework Statement

Charge q1 = +8.36 μC is fixed at the origin and charge q2 = -4.28μC is fixed on the +x-axis, 0.371m from the origin.

(a) Find the direction and magnitude of the electric field at a point P that has coordinates (0.466, 0.466) m.

(b) Find the direction and magnitude of the force on a -2.00 μC charge placed at the point P. (Please state the direction as an angle measured counterclockwise from the positive x-axis.)

Homework Equations

E = Kq/r^2

The Attempt at a Solution

Find θ1 = atan(0.466/0.466) = 45 degrees
θ2 = atan(0.466/0.095) = 78.48 degrees

I figured you just add the two vectors. For some reason I don't know how to... What is confusing me is that a can't use -4.28μC, for example, as the actual value. I think I need to use E=kq/r2 Here's what the diagram looks like

I really appreciate any helpEDIT:

I got the first part. It is attached
Would the second part just be F=Eq?

[/B]

 

[jedishrfu]

You should review this as its important.

Bascially convert the two vectors into components along the x and y-axis and go from there.

 

[josh12399]

You should review this as its important.

Bascially convert the two vectors into components along the x and y-axis and go from there.

But what values should I be using?

 

[SammyS]

Homework Statement

Charge q1 = +8.36 μC is fixed at the origin and charge q2 = -4.28μC is fixed on the +x-axis, 0.371m from the origin.

(a) Find the direction and magnitude of the electric field at a point P that has coordinates (0.466, 0.466) m.

(b) Find the direction and magnitude of the force on a -2.00 μC charge placed at the point P. (Please state the direction as an angle measured counterclockwise from the positive x-axis.)

Homework Equations

E = Kq/r^2

The Attempt at a Solution

Find θ1 = atan(0.466/0.466) = 45 degrees
θ2 = atan(0.466/0.095) = 78.48 degrees

I figured you just add the two vectors. For some reason I don't know how to... What is confusing me is that a can't use -4.28μC, for example, as the actual value. I think I need to use E=kq/r2 Here's what the diagram looks like

I really appreciate any help
[/B]

Hello josh12399 . Welcome to PF .

The resultant you have for E₁ + E₂ looks to be correct providing that you used correct magnitudes for E₁ and E₂. (You have placed the vectors in a rather unusual position relative to point P.)

What did you get for the magnitudes of E₁ and E₂ ?

 

[josh12399]

Hello josh12399 . Welcome to PF .

View attachment 103390

The resultant you have for E₁ + E₂ looks to be correct providing that you used correct magnitudes for E₁ and E₂. (You have placed the vectors in a rather unusual position relative to point P.)

What did you get for the magnitudes of E₁ and E₂ ?

To be honest I have no idea what to use for the magnitude. I tried a bunch of different things and got totally different answers.

I thought of splitting them up into E_X1, E_Y1, E_X2 and E_Y2, but I don't know what the actual magnitude should be. Should it be (k*q*cosθ)/r² for the x and (k*q*sinθ)/r² for the y?

 

[SammyS]

To be honest I have no idea what to use for the magnitude. I tried a bunch of different things and got totally different answers.

I thought of splitting them up into E_X1, E_Y1, E_X2 and E_Y2, but I don't know what the actual magnitude should be. Should it be (k*q*cosθ)/r² for the x and (k*q*sinθ)/r² for the y?

Use the following:

E = Kq/r²

for the electric field (magnitude) due to each charge.

 

[josh12399]

Use the following:

for the electric field (magnitude) due to each charge.

For each component (x and y)? Or should I just use the pythagorean theorem to find the diagonal distance from the charge to P?

 

[SammyS]

For each component (x and y)? Or should I just use the Pythagorean theorem to find the diagonal distance from the charge to P?

... just use the Pythagorean theorem to find the diagonal distance from the charge to P

 

[josh12399]

... just use the Pythagorean theorem to find the diagonal distance from the charge to P

E₁ = 1.730*10⁵ N/C
E₂ = -1.701*10⁵ N/C

Now I take the X and Y components using sine and cosine?

 

[SammyS]

E₁ = 1.730*10⁵ N/C
E₂ = -1.701*10⁵ N/C

Now I take the X and Y components using sine and cosine?

Yes.