Question

An unknown charge is repelled by a force of 40 newtons when it is at a distance of 5.0 cm from a charge of 40 microcoulombs. Find the magnitude of the unknown charge.

Answer 1

Electric force

$F=\frac{kq_1q_2}{r^2}$

$40=\frac{9\times10^9\times40\times10^{-6}\times q_2}{0.05^2}$

$q_2=2.77\times10^{-7}C$