Question

A charge, q1, of +15 micro-coulombs is located at x = 0, y = 10 cm, a charge q2 of -42 micro-coulombs is located at x = 0, y = -3.9 cm, an unknown charge of q3, is located at x =- 4.1 cm, y = 0 cm, and a charge, q4, -8 micro-coulombs is located at x = +13.9 cm, y = 0 cm. The direction of the total electric force on q4 is 127.8 degrees from the +x axis, counter-clockwise. What is the unknown charge, q3, in micro-coulombs? If negative, include a negative sign in your answer.

Answer 1

If distance between two charges q1 and q2 is r then force on each charge is -

F=kq1q2/r^{​​​​​​2}

Where k=8.99x10⁹N-m²/c^{​​​​​2}

if both charges are positive or negative then force acting on charges are repulsive.

And both charges are opposite sign then force acting on charges are attractive