# MCQ problem

1. Sep 10, 2007

### neelakash

1. The problem statement, all variables and given/known data

Three rigid rods are joined to form an equilateral triangle ABC of side 1m.Three particles carrying charge 1C are placed at the vertices.The whole system is in equilibrium in an inertial frame.What is the magnitude of the net force on each of the charges?

2. Relevant equations
3. The attempt at a solution

This may not be a simple question as it looks at first.In fact,it is an MCQ type question with four answers given from where we are to select the correct one.

The answer is zero.
Since the system is in equilibrium,the charges should also be in equilibrium too.
Hence,net force on each charge is to be zero.And that is the answer.

But what about the Coulomb's force and all that?They are there.And here we must assume external forces of equal magnitude acting over the charges in appropriate direction so that no net force acts on the system.

It should not be surprising to assume external forces if we recall the Earnshaw's theorem.

I think my logic is OK.

Please respond and let me know if I am correct.

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