I won't say much about the detailed process, just a few key points. First of all, we should make clear the meaning of E=-kQ/r, which refers to the electric potential energy of a point far away from the point charge r, and when you say 2/E, it refers to the electric potential energy of a point far away from the point charge 2/r. The difference between the two is 2/E, that is, the object can finally stop at a distance of 2/r from point R. The key is that the potential near the point charge is not 0! So the potential energy of the object near the point charge is not 0! This is not a contradiction between mathematics and physics, but that you have not considered it. ) If the farther the object is from the point charge, the greater the potential, indicating that the two charges are different, then the potential near the point charge at this time =q* potential, which is negative.

Give three numbers, Er= 10J, Er/2=5J, and e =-2J near the point charge. Given the kinetic energy of 5J, it can be from R to r/2, or from the vicinity of point charge to the place where r/2 is not reached. Good understanding. If the objects are farther away from the point charge, the greater the electric potential energy, indicating that they have different charges, and the electric potential energy of objects close to the point charge is negative, and vice versa. So if you give him kinetic energy of 10J, it is impossible for him to go from R to point charge! Your assumptions are w and W/2. You use contradiction to verify contradiction, and the result is of course contradiction.

Hope to adopt \ (o)/~