Question Detail

Positions: Q1(-0.6,0), Q2(0.6,0), Q3(0,0.8). Distance from Q1 to Q3 = sqrt(0.62+0.82)=1.0 m; same for Q2 to Q3. Force on Q3 from Q1 (repulsive, both would-be positive... Q1 positive, Q3 positive => repel, pushes Q3 away from Q1): direction (0.6,0.8). Force on Q3 from Q2 (Q2 negative, Q3 positive => attract, pulls Q3 toward Q2): direction (0.6,-0.8). Both forces have equal magnitude F = k|Q1||Q3|/r2 = (9x109)(6x10-6)(4x10-6)/1 = 0.216 N. Adding the vector components: y-components cancel (0.8F - 0.8F = 0); x-components add (0.6F+0.6F=1.2F). Net force = 1.2 x 0.216 = 0.259 N in the +x direction, i.e. approximately 0.26i N.