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## Homework Statement

A charge q1 = +8.15 muC is at the origin, and a charge q2 = -3.70 muC is on the x-axis 0.52 m from the origin. Find the electric field strength at point P, which is on the y-axis 0.61 m from the origin.

Answer = [1.613 x 10^5 N/C at 77.979 degrees]

## Homework Equations

E = kQ/r^2

k = 9.0 x 10^9

tan o = Ey / Ex (?)

C^2 = A^2 + B^2 (?)

Ex = E1 cos 30 (?)

Ey = E2 - E1 sin 30 (?)

## The Attempt at a Solution

I used the Pythagorean Theorem to figure out the distance from P to q2, which gave me 0.8 m.

I then went to use E to find E1, which I inputted as

((9x10^9)x(3.7x10^-6))/(0.8^2) = 5.2 x 10^4 N/C

Then E2 as

((9x10^9)x(8.15x10^-6))/(0.61^2) = 2.0 x 10^5 N/C

From there:

Ex = E1 x cos 30 = 4.5 x 10^4 N/C

Ey = (E2 - E1) x sin 30 = 7.4 x 10^4 N/C

Then I used Pythagorean Theorem again, thus getting:

E = Square root (4.5^2 + 7.4^2) x 10^4 = 8.7 x 10^4 N/C

Where did I go wrong? or did I do it incorrectly?

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