## anonymous 4 years ago Can anybody help me out here, or guide me where to start? In the image, the net electrostatic force in Qa is equal to 0, if Qa = +1.00 nC, what is the magnitude of Q0

1. anonymous

|dw:1326996252832:dw|

2. JamesJ

Find the force acting on Qa from each of the other three charges, using Coloumb's law. Sum them up and set it equal to zero. This will enable you to find Q_0.

3. anonymous

How can I know the distance between Qa and Q0?

4. JamesJ

Pythagorus' Theorem. Call that distance r. Then $r^2 = (2a)^2 + (-2a)^2 = 8a^2$ hence as r is positive, $r = \sqrt{8}a = 2\sqrt{2}a$

5. anonymous

pythagorus theorem wont do, its not making a right angled triangle, use the point distance formula

6. JamesJ

It is making a right-angled triangle with respect to the coordinate directions. And that is exactly how we derive the formula for distance in Euclidean space.

7. anonymous

we can directly use the , point distance formula here http://upload.wikimedia.org/wikipedia/en/math/4/0/8/408e1a8e214282114e49fc9f2abee36d.png

8. JamesJ

Yes, it's the same thing.

9. anonymous

Thanks for your replies, but I dont have a value for a

10. anonymous

you have to get the ans in terms of a in this