How this calculated using Coulomb law

Example 21.4 Comparing electric and gravitational forces A small plastic sphere is charged to 10 nC. It is held 1.0 cm above a small glass bead at rest on a table. The bead has a mass of 15 mg and a charge of +10 nC. Will the glass bead \"leap up\" to the plastic sphere? PREPARE We'll model the bead and the sphere as point charges and measure distances between their centers. There is an attractive electric force from the sphere that will tend to pull the bead upward. If this force is greater than the downward weight force, then the bead will leap upward. The pictorial representation in Figure 21.179 establishes a yaxis, identies the plastic sphere as ql and the glass bead as qg, and shows a free-body diagram. The glass bead will rise if F1 on 2 > w; if F1 0112