Question

A negative charge of -3.0 x 10^-6 C and a positive charge of 4.0 x 10^-6 C are separated by a distance of 3mm. What is the force on the negative charge? (magnitude and direction)

Answer 1

Сharges with opposite signs attract each other, so the Coulomb's force would be directed to the positive charge.
F = k |q₁||q₂|/R² = 8.99 x10⁹ [Nm²/C²]*|-3.0 x 10^-6|[C]*|4.0 x 10^-6|[C]/(3x10^-3)²[m²] = 11.98 x 10³ N.