JEE Main & Advanced Physics NLM, Friction, Circular Motion Sample Paper Topic Test - Friction

  • question_answer
    Two masses A and B of 10 kg and 5 kg are connected with a string passing over a frictionless pulley fixed at the corner of a table (as shown in figure). The coefficient of friction between the table and block is 0.2. The minimum mass of C that maybe placed on A to prevent it from moving is equal to

    A) 15 kg    

    B) 10 kg

    C) 5 kg                             

    D) zero

    Correct Answer: A

    Solution :

    Let T be the tension in the string,
    f = frictional force between block A and table,
    m = minimum mass of C.
    For the just motion of block A on table
                \[T=\,f=\mu R=\,\mu (m+m')\,g\]
    = 0.2(10+m')g               …...… (i) 
    For the just motion of block B
    T = 5g                          ...…… (ii)
    From Eqs.(i) and (ii), we get
    \[5g=0.2\text{ }\left( 10+m' \right)\text{ }g\]
    \[M'=\left( 52 \right)/0.2\text{ }=15\text{ }kg.\]

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