NEET Sample Paper NEET Sample Test Paper-41

  • question_answer
    A steel wire is suspended vertically from a rigid support. When loaded with a weight in air, it extends by \[{{l}_{a}}\] and when the weight is immersed completely in water, the extension is reduced to\[{{l}_{w}}\]. Then the relative density of:

    A) \[\frac{{{l}_{a}}}{{{l}_{w}}}\]                        

    B) \[\frac{{{l}_{a}}}{{{l}_{a}}-{{l}_{w}}}\]

    C) \[\frac{{{l}_{w}}}{{{l}_{a}}-{{l}_{w}}}\]                    

    D) \[\frac{{{l}_{w}}}{{{l}_{a}}}\]

    Correct Answer: B

    Solution :

    Case-I (in air) \[Y=\frac{FL}{A\Delta l}=\frac{FL}{A{{l}_{a}}}\therefore {{F}_{Trust}}=v\,\rho g\] \[=\frac{v\,\rho g}{A{{l}_{a}}}\]                                               ?(1) Case - 2 when the lead is immersed in a liquid, \[{{W}_{net}}={{W}_{b}}-Thrust\] \[=V\,\rho g\,-V\times {{\rho }_{w}}\times g\] \[=V\,\rho g\,-V\times 1\times g\] \[=\frac{\left( V\,\rho g\,-V\times 1\times g \right)L}{A{{l}_{w}}}\]             ?.(2) Y is same, because material is same (1) = (2) we get \[\rho =\frac{{{l}_{a}}}{{{l}_{a}}-{{l}_{w}}}\]


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