[Electrical force] 2 balls hanging from ceiling

[Delta2]

but where is the electrical force and what about all the rest of information (mass, charge, distance)

Well this question is some sort of trap like question it gives a lot of irrelevant information but the only piece of information you need to answer it , is that the system is in equilibrium.

However if you want to determine Fbody or Fceiling the rest information will come into play.

 

[sea333]

However if you want to determine Fbody or Fceiling the rest information will come into play.

Do I need to determine it to solve this exercise?

 

[Delta2]

Do I need to determine it to solve this exercise?

Nope.

 

[sea333]

That is a very strange exercise with a lot of redundant information it seems

 

[jbriggs444]

but where is the electrical force and what about all the rest of information (mass, charge, distance)

The electrostatic force from the bottom ball acts on the top ball.
The electrostatic force from the top ball acts on the bottom ball.

The force of gravity on the top ball acts on the top ball
The force of gravity on the bottom ball acts on the bottom ball.

The force of the ceiling on the top string acts on the top string.
The force of the top string on the ceiling acts on the ceiling

The force of the string on the top ball acts on the top ball.
The force of the top ball on the top string acts on the top string.

The force of the top ball on the bottom string acts on the bottom string.
The force of the bottom string on the top ball acts on the top ball.

The force of the bottom string on the bottom ball acts on the bottom ball.
The force of the bottom ball on the bottom string acts on the bottom string.

We ignore gravity and electrostatic forces acting on both strings because the strings are uncharged and are negligibly massive.

If you want to know the net force on the top string, you add up the forces on the top string.

You can do this the hard way -- solve a bunch of simultaneous equations and find that everything cancels.
Or you can do it the easy way -- Newton's second law. $\sum F=ma$ and a = 0.

 

[sea333]

I am satisfied with easier route for this exercise.

 

[haruspex]

I do object to the wording of the question. Despite specifying "force", it is natural to assume the question is asking about tension. It should specify "net force".

 

[kuruman]

I do object to the wording of the question. Despite specifying "force", it is natural to assume the question is asking about tension. It should specify "net force".

Yes, the wording is vague but the intent of the author may have been lost in translation. "How big is a force that is functioning on a thread?" is looking for a tension, but in which thread? There are two of them.

 

[sea333]

I can paste the text in my native language but I don't know if it would help

 

[jbriggs444]

Yes, the wording is vague but the intent of the author may have been lost in translation. "How big is a force that is functioning on a thread?" is looking for a tension, but in which thread? There are two of them.

The net force on both is identical. It is not tension that is being asked for.

 

[kuruman]

The net force on both is identical. It is not tension that is being asked for.

I am not convinced that "How big a force that is functioning on a thread" is equivalent to "What is the net force on a thread", but OK. I will not pursue this any further.