Question

A block has been placed on a inclined plane with the slope angle $\theta$, block slides down the plane at constant speed. The coefficient of kinetic friction is equal to

• A. $\sin \theta$
• B. $\cos \theta$
• C. $g$
• D. $\tan \theta$

Answer 1

Answer: (D)

The acceleration is nullified by force of kinetic friction/mass
mg sin$\theta$ is force downwards.
${\mu }_k$ is the coefficient of kinetic friction.
${\mu }_{k}mg\cos \theta$ is force acting upwards.
$\therefore mg\sin \theta ={\mu }_{k}mg\cos \theta =$ mass $\times$ acceleration $=0$ as $v$ is constant
$\therefore {\mu }_k=\tan \theta$.