RAJASTHAN PMT Rajasthan - PMT Solved Paper-1999

  • question_answer
    When a force F is applied on a wire of length L and radius r, extension produce is \[l\]. If same force F is applied on the same material wire of length 2L and radius 2r, then extension will be:

    A)  \[l\]                      

    B)         \[2l\]                                   

    C)  \[l/2\]                                 

    D)         \[4l\]

    Correct Answer: C

    Solution :

    Young's elasticity coefficient \[\Upsilon =\frac{Fl}{\pi {{r}^{2}}\Delta l}\] wires are of same material so their Young's coefficient will be same. \[\therefore \frac{{{F}_{1}}{{l}_{1}}}{\pi r_{1}^{2}\Delta {{l}_{1}}}=\frac{F{{ & }_{2}}{{l}_{2}}}{\pi r_{2}^{2}\Delta {{l}_{2}}}\] \[\frac{F\times L}{\pi {{r}^{2}}\times l}=\frac{F\times 2L}{\pi {{(2r)}^{2}}\times \Delta {{l}_{2}}}\] \[\Delta {{l}_{2}}=l/2\] Extension produced in the 2nd wire \[=\frac{l}{2}\]


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