question_answer

    A block rests on a rough inclined plane making an angle of\[30{}^\circ \]with the horizontal. The coefficient of static friction between the block and the plane is 0.8. If the frictional force on the block is 10 N, the mass of the block Jin kg) is (take\[g=10\text{ }m/{{s}^{2}})\]

A)  2.0                                        

B)  4.0

C)  1.6                                        

D)  2.5

Correct Answer: A

Solution :

                Let the mass of block be\[m\]. Frictional force in rest position                 \[F=mg\sin 30{}^\circ \] [This is static frictional force and may be less than the limiting frictional force]                 \[10=m\times 10\times \frac{1}{2}\] \[\therefore \]  \[m=\frac{2\times 10}{10}=2\,kg\]