• # question_answer 11) A block of mass 8 kg rests on a rough inclined plane of angle${{30}^{o}}$and$\mu =\frac{3}{4}$between the block and the plane. The value of the force of friction is: [Take$g=10\,m/{{s}^{2}}$] A)  51.96 N                     B)  40 NC)  28 N                          D)  54.8 N

Solution :

Limiting friction $={{f}_{L}}=\mu \,mg\,\cos {{30}^{o}}=51.96\,N$But $mg\sin {{30}^{o}}<{{f}_{L}},$so friction is static in nature and the block it not moving. Therefore, $F=mg\sin {{30}^{o}}=40N.$ Hence, the correction option is [b].

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