JEE Main & Advanced Sample Paper JEE Main Sample Paper-20

  • question_answer
    A block of mass m is attached with massless spring offeree constant k. The block is placed over a fixed rough inclined surface for which the coefficient of friction is \[\mu =3/4\]. The block of mass m is initially at rest. The block of mass M is released from rest with spring in unstretched state. The minimum value of M required to move the block up the plane is (neglect mass of string and pulley and friction in pulley.)

    A)  \[\frac{3}{5}m\]                                              

    B)  \[\frac{4}{5}m\]

    C)  \[\frac{6}{5}m\]                                              

    D)  \[\frac{3}{2}m\]

    Correct Answer: A

    Solution :

     As long as the block of mass m remains stationary, the block of mass M released from rest comes down by \[\frac{2Mg}{K}\](before coming it rest momentarily again). Thus the maximum extension in the spring is \[x=\frac{2Mg}{k}\]                                ??.(1) For block of mass m to just move up the incline \[kx=mg\sin \theta +\mu mg\cos \theta \]          ???..(2) \[2Mg=mg\times \frac{3}{5}+\frac{3}{4}mg\times \frac{4}{5}\]  or \[M=\frac{3}{5}m\]


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