Halliday, Resnick & Walker — Coulomb's Law: Problem 20

Figure 21-16a shows charged particles 1 and 2 that are fixed in place on an x axis. Particle 1 has a charge with a magnitude of \(|q_1| = 8.00e\). Particle 3 of charge \(q_3 = +7.00e\) is initially on the x axis near particle 2. Then particle 3 is gradually moved in the positive direction of the x axis. As a result, the magnitude of the net electrostatic force \(\vec{F}_{2,net}\) on particle 2 due to particles 1 and 3 changes. Figure 21-16b gives the x component of that net force as a function of the position x of particle 3. The scale of the x axis is set by \(x_s = 0.80 \text{ m}\). The plot has an asymptote of \(F_{2,net} = 1.5 \times 10^{-25} \text{ N}\) as \(x \to \infty\). As a multiple of e and including the sign, what is the charge \(q_2\) of particle 2?