On Sun, 10 Jul 2016 13:44:25 -0400, kensi wrote:

> On 09/07/2016 3:20 PM, Nadegda wrote:
>> On Sat, 09 Jul 2016 06:44:37 -0700, Colonel Edmund J. Burke wrote:
>>> On 7/7/2016 6:38 AM, Sergio wrote:
>>>> Two identical point charges are held a distance d apart by a non
>>>> conducting string with tension T. If a third identical point charge
>>>> is fixed at a distance of d/2 from both of the first two point
>>>> charges then what will be the new tension in the string ?
>>>>
>>>> a) T b) 2T c) 3T d) 4T e) 5T
>>>
>>> When I did this equation, it ended up being the equivalence of "A
>>> BLACK RUSSIAN," or around nine inches.
>>> Discuss.............
>>
>> I'm guessing that you're wrong, but string theory is kensi's
>> department, so I'll reserve judgment until I hear from her.
>
> In fact, he's "not even wrong", or even making any sense. Also, that's
> not really string theory, it's just electrostatics. And the correct
> answer to the original problem is e. The tension on the string is equal
> to the electrostatic repulsion force, given the system is in static
> equilibrium, and one of the end charges thus felt a force of T from the
> other end charge pushing it away. The new charge at the midpoint is half
> as far away, and the electric force is inverse-square, so that adds a
> force of 4T for a total of 5T from both other charges.

Heh. Shame Bill Jillians beat you to the answer -- on the other hand,
unlike him, you've shown your work.