The potential energy of this system is equal to the work required to remove
the points to infinity. This can be done in a number of ways, but the
result is always the same, and equal to:
but and , so:
The centre of mass of a free system like this remains at rest as long as there are(b) If the particles are released simultaneously, where will they collide?
no external forces, so the particles must collide at their centre of mass, which is
at the centre of the equilateral triangle.