JEE Main & Advanced Physics NLM, Friction, Circular Motion Question Bank Critical Thinking Questions

  • question_answer
    A block of mass 2 kg rests on a rough inclined plane making an angle of 30° with the horizontal. The coefficient of static friction between the block and the plane is 0.7. The frictional force on the block is            [IIT 1980; J & K CET 2004]                

    A)                 9.8 N                     

    B)                 \[0.7\times 9.8\times \sqrt{3}\,N\]                

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

    D)                    \[0.8\times 9.8\,N\]

    Correct Answer: A

    Solution :

                        Limiting friction \[{{F}_{l}}=\mu \ mg\cos \theta \]                 \[{{F}_{l}}=0.7\times 2\times 10\times \cos 30{}^\circ =12\ N\](approximately) But when the block is lying on the inclined plane then component of weight down the plane \[=mg\sin \theta \] \[=2\times 9.8\times \sin 30{}^\circ =9.8\ N\]                 It means the body is stationary, so static friction will work on it                 \[\therefore \] Static friction = Applied force = 9.8 N                


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