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## Main Question or Discussion Point

Hi everyone, I don't know how I manage it but I've gone and confused myself about something which I was fairly confident about right before an exam... again!

So here's the deal.

Let's imagine two particles A and B which have charge Q and q respectively and are separated by a distance r (I know, imaginative right?).

Now, if A is held in place and B is released then I can calculate its maximum velocity through these steps:

1) Get the EPE of B [itex]\frac{k_{e}Qq}{r}[/itex]

2) Assume all of the EPE becomes KE and so [itex]\frac{m_{B} v_{max}^2}{2} = \frac{k_{e}Qq}{r}[/itex]

3) Rearrange for v and job done

But whilst I've been happily doing this for a while, I realised that A is losing EPE as well. If A is being held stationary and is losing EPE, but only B is gaining KE then surely the KE gain of B ought to be the sum of the EPE loss of A and B otherwise energy conservation is violated.

But as all the calculations I've ever done have never shown this to be the truth I am doubting this thought.

So, I had a quick discussion with someone and we came to the conclusion that maybe we had a more fundamental misunderstanding of EPE and that in reality the

So, anyone want to jump in and help me out?!

Cheers,

James

So here's the deal.

Let's imagine two particles A and B which have charge Q and q respectively and are separated by a distance r (I know, imaginative right?).

Now, if A is held in place and B is released then I can calculate its maximum velocity through these steps:

1) Get the EPE of B [itex]\frac{k_{e}Qq}{r}[/itex]

2) Assume all of the EPE becomes KE and so [itex]\frac{m_{B} v_{max}^2}{2} = \frac{k_{e}Qq}{r}[/itex]

3) Rearrange for v and job done

But whilst I've been happily doing this for a while, I realised that A is losing EPE as well. If A is being held stationary and is losing EPE, but only B is gaining KE then surely the KE gain of B ought to be the sum of the EPE loss of A and B otherwise energy conservation is violated.

But as all the calculations I've ever done have never shown this to be the truth I am doubting this thought.

So, I had a quick discussion with someone and we came to the conclusion that maybe we had a more fundamental misunderstanding of EPE and that in reality the

*system*has an EPE given by equation 1. When B is allowed to move from A, the EPE of the system decreases to zero as the KE of B increases by the same amount.So, anyone want to jump in and help me out?!

Cheers,

James