Question

Figure 21.5 Two small insulating spheres are attached to silk threads. The spheres have equal masses of 40 g, and have electric charges of q1 = +2.0 ?C and q2 = -2.0 ?C. The spheres are brought into the initial positions shown in Fig. (a), with a vertical separation of 15 cm between them. In Fig. 21.5, the tension in the lower thread in Fig. (a) is closest to: Figure 21.5 Two small insulating spheres are attached to silk threads. The spheres have equal masses of 40 g, and have electric charges of q1 = +2.0 C and q2 = -2.0 C. The spheres are brought into the initial positions shown in Fig. (a), with a vertical separation of 15 cm between them. In Fig. 21.5, the tension in the lower thread in Fig. (a) is closest to: 1.2 N 1.4 N 1.6 N 2.0 N 1.8 N

Answer 1

The question refers to the configuration on the left side of the figure, labeled (a), right? Configuration (b) is for another problem?

Anyway, for configuration (a) there are two forces acting on q₂, gravity and the Coulomb force, and they act in opposite directions. The tension in the thread is the algebraic sum of those forces.

Gravitational force is mg = (0.04 kg)(9.81 m/s²) = 0.3924 N.

Coulomb force is kq₁q₂/r² = (8.987 * 10⁹ N-m²/C²)(2 * 10^-6 C)(-2 * 10^-6 C)/(.15m)² = -1.598 N

Tension is the magnitude of the sum: 1.205 N