AIIMS 2017 Physics Coulomb's Law and Friction MCQ Question

To maintain equilibrium, the electrostatic force between the fixed charge (10 mC = 10 × 10⁻³ C) and the block must balance the maximum static friction force. The maximum static friction $F_f$ is given by $F_f = \mu m g$, where $\mu = 0.5$, $m = 0.08 \, \text{kg}$, and $g \approx 9.8 \, \text{m/s}²$, resulting in $F_f \approx 0.4 \, \text{N}$. Using Coulomb's law, $F_e = k \frac{|q_1 q_2|}{r^2}$, we find that the charge on the block $q_2$ must lie within the range of approximately $-4 \times 10^{-9} \, \text{C}$ to $4 \times 10^{-9} \, \text{C}$ to maintain equilibrium, confirming option A. Other options are incorrect as they suggest ranges that do not satisfy the balance of forces based on the given parameters.