Coulomb's Law: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Coulomb's Law. Understanding the underlying formula is key to arriving at the correct answer below:

For the system to be in equilibrium, the net force on any charge must be zero. Considering a charge $Q$ at the end, $F_{\text{net}} = \frac{k Q^2}{x^2} + \frac{k Q q}{(x/2)^2} = 0$. Solving this yields $q = -Q/4$.