BHU PMT BHU PMT (Mains) Solved Paper-2009

  • question_answer
    The block A in figure weighs 100 N. The coefficient of static friction between the block and table is 0.25. The maximum weight of block B for which the system is in equilibrium is

    A)  25 N                                     

    B)  30 N

    C)  35 N                                     

    D)  40 N

    Correct Answer: A

    Solution :

                     The frictional force\[{{F}_{S}}\]on block A, when it tends to move is\[{{F}_{S}}={{\mu }_{S}}R={{\mu }_{S}}{{W}_{A}}=0.25\times 100=25\,N\]                 For equilibrium of block A, \[{{T}_{1}}={{F}_{S}}=25\,N\]                                                               ...(i)                 and for equilibrium of block B \[{{T}_{1}}={{T}_{2}}\cos {{45}^{o}}\]and \[{{W}_{B}}={{T}_{2}}\sin {{45}^{o}}\]                                ...(ii)                 From Eq (ii)                 \[{{W}_{B}}={{T}_{2}}\sin {{45}^{o}}=\left( \frac{{{T}_{1}}}{\cos {{45}^{o}}} \right)\sin {{45}^{o}}\]                 \[={{T}_{1}}\tan {{45}^{o}}={{T}_{1}}\]                                 \[\therefore \]  \[{{W}_{B}}={{T}_{1}}=25N\]


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