When is an Electric Field eqn set as - or + ?

[PerpetuallyConfused]

Homework Statement

Two point charges are placed on the x axis.(Figure 1)The first charge, q1 = 8.00 nC , is placed a distance 16.0 m from the origin along the positive x axis; the second charge, q2 = 6.00 nC , is placed a distance 9.00 m from the origin along the negative x axis.

Find the electric field at the origin, point O.

Give the x and y components of the electric field as an ordered pair. Express your answer in Newtons per coulomb to three significant figures. Keep in mind that an x component that points to the right is positive and a y component that points upward is positive.

Homework Equations

I know I have to use the equation E = kQ/r^2 and I have to calculate E for each charge.

The Attempt at a Solution

So far I have E2 = kQ2/r2^2 and E1 = - kQ1/r1^2
I am confused on how I know when to set E = kQ/r^2 as positive or negative?

 

[cnh1995]

Homework Statement

Two point charges are placed on the x axis.(Figure 1)The first charge, q1 = 8.00 nC , is placed a distance 16.0 m from the origin along the positive x axis; the second charge, q2 = 6.00 nC , is placed a distance 9.00 m from the origin along the negative x axis.

Find the electric field at the origin, point O.

Give the x and y components of the electric field as an ordered pair. Express your answer in Newtons per coulomb to three significant figures. Keep in mind that an x component that points to the right is positive and a y component that points upward is positive.
View attachment 220767

Homework Equations

I know I have to use the equation E = kQ/r^2 and I have to calculate E for each charge.

The Attempt at a Solution

So far I have E2 = kQ2/r2^2 and E1 = - kQ1/r1^2
I am confused on how I know when to set E = kQ/r^2 as positive or negative?

Conventionally, the field due to a positive charge is directed away from the charge and that due to a negative charge is directed towards the charge.

Assume any direction to be positive and find the resultant. Its sign will tell you whether it is along the positive direction or the negative direction.

 

[kuruman]

Draw two arrows at the origin indicating the electric field due to each charge. Arrows to the right are positive, arrows to the left are negative. Add the two arrows as vectors.

 

[kuruman]

Assume any direction to be positive ...

The coordinate system posted by OP is already chosen so that positive x and y are "to the right" and "up".