JEE Main & Advanced JEE Main Paper (Held On 12-Jan-2019 Evening)

  • question_answer
    A load of mass M kg is suspended from a steel wire of length 2 m and radius 1.0 mm in Searle's apparatus experiment. The increase in length produced in the wire is 4.0 mm. Now the load is fully immersed in a liquid of relative density 2. The relative density of the material of load is 8. The new value of increase in length of the steel wire is [JEE Main Online Paper Held On 12-Jan-2019 Evening]

    A) 4.0 mm                                    

    B) zero      

    C) 5.0 mm                        

    D)   3.0 mm.           

    Correct Answer: D

    Solution :

    Let \[\rho \]and \[\sigma \]be the density of the liquid and material of the load respectively. In first case, the extension in the wire is \[x=Mg/k=V\rho g/k\]                             ?.(i) When the load is immersed in the liquid, up thrust + internal force due to extension in wire = weight of the load \[\Rightarrow V\sigma g+k{{x}_{1}}=V\rho g\Rightarrow {{x}_{1}}=Vg(\rho -\sigma )/k\] Using (i) and (ii), \[{{x}_{1}}=\frac{Vgx}{Vg\rho }(\rho -\sigma )=x\left( 1-\frac{\sigma }{\rho } \right)=4\times \left( 1-\frac{2}{8} \right)=3mm\]


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