Question

A charge of -3.66C is fixed at the center of a compass. Two additional charges are fixed on the circle of the compass (radius = 0.0978 m). The charges on the circle are -4.04C at the position due north and +6.20C at the position due east. What is (a) the magnitude and (b) direction of the net electrostatic force acting on the charge at the center? Specify the direction as an angle relative to due east.

I get (a) to be 25.5, but (b) I cannot get, I keep getting -56.9 degrees. But it is wrong. why?

Answer 1

Let me check your angle: If the reference is East, then

tanTheta=-4.04/6.20

Theta=-.578 radians or -33.1 deg

and the angle is S of E

Do a little thinking on how I simplified the angle to just those two numbers..

Answer 2

Somehow, I got the right magnitude, but my x and y are different. my x=-21.35 and y=13.9 how?

Answer 3

I am not certain what your x and y are, what was given was forces along N-S, and E-W.

the N-S force is not as strong as the E-
w because of the charge magnitude.

Not knowing what x, y is, my guess is that x is the force along E, and y is the force S.
theta=arctan(13.9/21.35)=exactly the answer I got above.