JEE Main & Advanced Physics Gravitation / गुरुत्वाकर्षण Question Bank Mock Test - Gravitation and Mechanical Properties of Solid

  • question_answer
    Two wires are made of the same material and have the same volume. However, wire 1 has cross-sectional area \[A\] and wire 2 has cross-sectional area\[3A\]. If the length of wire 1 increases by Ax on applying a force \[F\], how much force is needed to stretch wire 2 by the same amount?

    A) \[F\]                                        

    B)  \[4F\]

    C) \[6F\]               

    D) \[9F\]

    Correct Answer: D

    Solution :

    [d] \[{{A}_{1}}{{l}_{1}}={{A}_{2}}{{l}_{2}}\] \[\Rightarrow {{l}_{2}}=\frac{{{A}_{1}}{{l}_{1}}}{{{A}_{2}}}=\frac{A\times {{l}_{1}}}{3A}\] \[\Rightarrow \frac{{{l}_{1}}}{{{l}_{2}}}=3\] \[\Delta {{x}_{1}}=\frac{{{F}_{1}}}{A\gamma }\times {{l}_{1}}\] \[\Rightarrow {{x}_{2}}=\frac{{{F}_{2}}}{3A\gamma }\times {{l}_{1}}\] Here \[\Delta {{x}_{1}}=\Delta {{x}_{2}}\] \[\frac{{{F}_{2}}}{3A\gamma }{{l}_{2}}=\frac{{{F}_{1}}}{A\gamma }{{l}_{1}}\Rightarrow {{F}_{2}}=3{{F}_{1}}\times \frac{{{l}_{1}}}{{{l}_{2}}}=3{{F}_{1}}\times 3=9F\]


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