AIIMS 2019 Physics Friction MCQ Question

When a body slides down a rough inclined plane at a constant velocity, the forces acting on it are balanced. The gravitational force component along the incline is given by $mg \sin \theta$ and the frictional force opposing this motion is $\mu mg \cos \theta$, where $\mu$ is the coefficient of friction. For equilibrium, these forces must be equal:

$$mg \sin \theta = \mu mg \cos \theta$$

Dividing both sides by $mg$ and rearranging gives $\mu = \tan \theta$. For an incline of $30^\circ$, $\tan 30^\circ = \frac{1}{\sqrt{3}}$, making option A correct. Other options are incorrect as they do not accurately represent the tangent of the angle, which is essential for calculating the coefficient of friction in this scenario.