Question

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

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

Answer 1

The correct option is D $tan\theta$

If $\mu$ be the coefficient of kinetic friction, then the friction force $f=\mu N$

Now , normal force $N=mg\cos \theta$ so $f=\mu mg\cos \theta$

In equilibrium, $mg\sin \theta =f=\mu mg\cos \theta$ or $\mu =\frac{\sin \theta }{\cos \theta }=\tan \theta$