Question Detail
Question
Two charges are located on the positive x-axis. q1=2x10-9 C is 2 cm from the origin, and q2=3x10-9 C is 4 cm from the origin. What is the magnitude of the total force exerted by these two charges on a charge q3=5x10-9 C located at the origin?
Correct Answer
Option B is the correct answer.
Detailed Explanation
F1 (from q1, r=0.02m) = k q1 q3/r12 = (9x109)(2x10-9)(5x10-9)/(0.02)2 = 9x10-8/4x10-4 = 2.25x10-4 N. F2 (from q2, r=0.04m) = (9x109)(3x10-9)(5x10-9)/(0.04)2 = 1.35x10-7/1.6x10-3 = 8.44x10-5 N. Both charges are positive and both push q3 in the same direction (away from them, i.e. toward -x), so the forces add: F_total = 2.25x10-4 + 0.844x10-4 = 3.09x10-4 N.
Hint
F1 (from q1, r=0.02m) = k q1 q3/r12 = (9x109)(2x10-9)(5x10-9)/(0.02)2 = 9x10-8/4x10-4 = 2.25x10-4 N.