Coulomb's Law Problems

[physics231]

I have a couple of Coulomb's Law problems.

1) A charge of 6.00 mC is placed at each corner of a square 0.100 m on each side. Determine the magnitude and direction of the force on each charge.

2) Two charges, -Q and -3Q (subscript 0 at the end of each Q),are a distance L apart. There two charges are free to move but do not because there is a third charge nearby. What must be the charge and placement of the third charge for the first two to be in equilibrium?

Any help is greatly appreciated. Thank you very much

[Päällikkö]

Please show what you've tried.
http://www.physicsforums.com/showthread.php?t=94379

[Ihelppeople]

I have a couple of Coulomb's Law problems.

1) A charge of 6.00 mC is placed at each corner of a square 0.100 m on each side. Determine the magnitude and direction of the force on each charge.

2) Two charges, -Q and -3Q (subscript 0 at the end of each Q),are a distance L apart. There two charges are free to move but do not because there is a third charge nearby. What must be the charge and placement of the third charge for the first two to be in equilibrium?

Any help is greatly appreciated. Thank you very much

Check your pm box. I can never understand why people will never help people and show them how to solve certain problems. You learn by being shown and then applying what you were given. You don't learn by spending hours trying to solve a problem. That time can be spent studying and or going over more problems so you can succeed.

[cupid.callin]

So you mean that "Einstein" should have asked someone about the photoelectric effect instead of wasting his whole life searching for it ???

That was the most useless advice ever!!!

[cupid.callin]

And for your question ... i cant solve it for you but yes some advide
for 1st, draw a big diagram (and please use a scale) and draw all the forces,

And find all net forces in a single plane, then find their net force!!!

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for second what do you think about the sign of charge?