Understanding Balloon Charges and Interactions

[t3rom]

Homework Statement

There are 5 balloons, A, B, C, D, and E. The following observations were made on the balloons: (I) Balloon A attracts balloon B and balloon A repels balloon C. (II) Balloon D attracts balloon B, and balloon D has no effect on balloon E. (III) A negatively-charged rod attracts both balloon A and balloon E. Figure out what are the charges on each of the balloons. There may be balloons where they have a neutral charge.

Relevant Equations

Like charges repel each other, unlike charges attract each other. Positively charged objects and neutral objects attract each other; and negatively charged objects and neutral objects attract each other.

Balloon A is + as negatively charged rod attracts it
Balloon B is - as Balloon A attracts it.
Since Balloon A (+) repels balloon C so it means Balloon C is +.
Balloon D attracts Balloon Balloon B (-) so it means Balloon D is +.
Balloon E is neutral as negatively charged objects and neutral objects attract each other.

Kindly check if this is correct.

Thank you!

 

[TSny]

Balloon D is +.
Balloon E is neutral

If D is + and E is neutral, would D and E affect each other?

 

[t3rom]

If D is + and E is neutral, would D and E affect each other?

That's exactly I'm confused about.

 

[TSny]

That's exactly I'm confused about.

This link might help.

 

[t3rom]

This link might help.

Why would the question say then "balloon D has no effect on balloon E"? In what scenario is this possible?

 

[haruspex]

Positively charged objects and neutral objects attract each other;

That reads as though positively charged objects would attract each other, and neutral objects attract each other. I guess you mean a positively charged object and a neutral object attract each other.
That's true, but it is worth bearing in mind that conductors with like charges can also attract each other under the right conditions. In the present question, it seems we are to take all the objects as nonconducting.

 

[t3rom]

That reads as though positively charged objects would attract each other, and neutral objects attract each other. I guess you mean a positively charged object and a neutral object attract each other.
That's true, but it is worth bearing in mind that conductors with like charges can also attract each other under the right conditions. In the present question, it seems we are to take all the objects as nonconducting.

So it means both D and E are neutral?

 

[TSny]

So it means both D and E are neutral?

Yes, but it's not clear to me that you have used the correct logic to obtain the charges of A, B, and C.

Balloon A is + as negatively charged rod attracts it

The attraction of balloon A to the negatively charged rod does not necessarily imply that A is positively charged. Balloon A could be neutral. You need to use some of the other given information to deduce whether or not A is charged.

Balloon B is - as Balloon A attracts it.

Even if balloon A were to carry a positive charge, it does not follow from this alone that B has to be negatively charged.

 

[TSny]

it is worth bearing in mind that conductors with like charges can also attract each other under the right conditions.

Yes. I think this is true for dielectric bodies also. A balloon that carries a large amount of positive charge could attract another balloon that carries a very small amount of positive charge if the balloons are near enough to each other. I'm sure we're supposed to neglect such quirks in this problem. But it's an interesting point that you have brought up.