question_answer

A block is placed on an inclined plane having angle of inclination \[\alpha \] If the block slide down the plane at a constant speed, then the coefficient of kinetic friction between block and inclined plane is equal to

A)  \[sin\,\,\alpha \]             

B)  \[\cos \,\,\alpha \]

C)  \[\tan \,\,\alpha \]                      

D)  None of these

Correct Answer: C

Solution :

As block is moving with constant speed, So,           \[\operatorname{F} =\,\,{{f}_{r}}\] \[\operatorname{mg}\,\,sin \alpha  = \mu \,mg\,\,cos \alpha \] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\mu  = tan \alpha \]