Question

two point charges totaling 7.00 exert a repulsive force of 0.100N on one another when separated by 0.703 m. what is the charge on each if the force is attractive? Smallest charge? Largest charge ?

Answer 1

charges repels so they are of same sign.

q1 + q2 = 7 x 10^-6

and F = k q1 q2 / r

0.1 = (9 x 10^9) (q1) (7 - q1) / (0.703^2)

- q1^2 + (7 x 10^-6) q1 = 5.49 x 10^-12

q1 = 6.1 x 10^-6 , 0.9 x 10^-6 C

Smaller charge = 0.9 x 10^-6 C

larger charge = 6.1 x 10^-6 C

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when force is attractive,

q1 - q2 = 7 x 10^-6 { q1 > q2}

0.1 = (9 x 10^9) (q2)(7 x 10^-6 + q2) / 0.703^2

q1^2 + (7 x 10^-6) q2 = 5.49 x 10^-12

q2 = 0.71 x 10^-6 C and 7.71 x10^-6 C

smaller charge = - 0.71 x 10^-6 C

larger charge = + 7.71 x 10^-6 C