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

  • question_answer
    A body of mass M is kept on a rough horizontal surface (friction coefficient \[\mu \]). A person is trying to pull the body by applying a horizontal force but the body is not moving. The force by the surface on the body is F, where                                                                                 [MP PET 1997]                

    A)                 \[F=Mg\]                

    B)                    \[F=\mu Mgf\]                

    C)                 \[Mg\le F\le Mg\sqrt{1+{{\mu }^{2}}}\]                

    D)                 \[Mg\ge F\ge Mg\sqrt{1+{{\mu }^{2}}}\]

    Correct Answer: C

    Solution :

                        Maximum force by surface when friction works                 \[F=\sqrt{{{f}^{2}}+{{R}^{2}}}=\sqrt{{{(\mu R)}^{2}}+{{R}^{2}}}=R\sqrt{{{\mu }^{2}}+1}\]                 Minimum force \[=R\] when there is no friction                 Hence ranging from R to \[R\sqrt{{{\mu }^{2}}+1}\]                 We get, \[Mg\le F\le Mg\sqrt{{{\mu }^{2}}+1}\]                               


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