Three Charges Problem: Sketching the Motion of Charges Released from Rest

[superconduct]

Roughly sketch the path of each charge if they are released from rest at the same time, and are allowed to move freely.

Here is my sketch :

The model answer:

Please tell me what is wrong with my sketch. Once R moves to the left side, PR and QR will be shorter than PQ. Attractive electric force on P outweighs the repulsive, similarly for Q. Shouldn't P and Q bend towards R instead of away? Consider when P, Q and R are collinear, there should be a net attractive force between P and Q?

 

[BruceW]

yeah, It is not very clear. I think what the book means is that to begin with, the particles will curve away from each other. And what the book doesn't say is that they will then start to curve back towards each other, when the negative charge gets in-between them.

So I think your answer is correct. (Although they might not curve all the way into each other, since they might be already going too fast, and never manage to meet with each other). But also, as the book says they will initially curve away from each other.

The book seems to expect the answer to what will happen initially. But it is not clear about this, so It is a badly-written question, I think.