Walker, Halliday & Resnick — Electric Potential: Problem 23

23 Identical \(50 \mu\text{C}\) charges are fixed on an \(x\) axis at \(x = \pm 2.0 \text{ m}\). A particle of charge \(q = -15 \mu\text{C}\) is then released from rest at a point on the positive part of the \(y\) axis. Due to the symmetry of the situation, the particle moves along the \(y\) axis and has kinetic energy \(1.2 \text{ J}\) as it passes through the point \(x = 0, y = 4.0 \text{ m}\). (a) What is the kinetic energy of the particle as it passes through the origin? (b) At what negative value of \(y\) will the particle momentarily stop?