Posted by **Megan** on Thursday, April 5, 2012 at 1:33pm.

Two spheres with charges of 4.00nC and 3.00nC are placed 0.500m apart. At what point between the two charges must the third charge of 2.00cN be placed so that the net electrostatic force acting on this charge is zero?

- physics -
**Elena**, Thursday, April 5, 2012 at 1:51pm
k •q1 •q3/x^2 = k •q2 •q3/(d-x)^2

q1 •q3 (d-x)^2 = k •q2 •q3• x^2

Solve for x

- physics -
**Elena**, Thursday, April 5, 2012 at 1:55pm
The second line

q1 •q3 (d-x)^2 = q2 •q3• x^2

- physics -
**Megan**, Thursday, April 5, 2012 at 2:26pm
Elena, for some reason I'm getting an answer of -3

(8.00 x 10^-12) x (d-x)^2 = (6.00 x 10^-12) x (x^2)

(d-x)^2/x^2 = 7.5 x 10^-1

(d-x)(d-x)/x^2 = 7.50 x 10^-1

x^2-x+0.25/x^2= 7.50 x 10^-1

then I get x = -3

Can you help! I'm not sure where i am going wrong.

- physics -
**Elena**, Thursday, April 5, 2012 at 3:54pm
q1 • (d-x)^2 = q2 • x^2

4•10^-9•(d-x)^2 = 3•10^-9•x^2

4(d^2 - 2•d•x + x^2) = 3•x^2,

x^2 - 4x + 1 = 0

x =2 ± sqrt(4-1) =2 ± 1.73.

x1 = 0.27 m, x2 =3.73m (falls out)

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