question_answer

A body of mass 2kg rests on a rough inclined plane making an angle \[{{30}^{o}}\] with the horizontal. The coefficient of static friction between the block and the plane is\[0.7\]. the frictional free on the block is:

A)  \[9.8\,N\]                    

B)  \[0.7\times 98\times \frac{1}{\sqrt{3}}N\]

C)  \[9.8\times \sqrt{3}\]              

D)  \[0.7\times 9.8\,N\]

Correct Answer: A

Solution :

From the figure.             \[{{F}_{S}}=\mu mg\,\cos \theta =0.7\times 2\times 9.8\times \sqrt{\frac{3}{2}}>9.8\]             \[{{F}_{S}}=mg\,\sin \theta =9.8\] Here, \[\theta ={{30}^{o}}\]