JEE Main & Advanced Physics Wave Mechanics Question Bank Self Evaluation Test - Mechanical Properties of Solids

  • question_answer
    A platform is suspended by four wires at its corners. The wires are 3m long and have a diameter of 2.0mm. Young's modulus for the material of the wires is 1,80,000 MPa. How far will the platform drop (due to elongation of the wires) if a 50 kg load is placed at the centre of the platform?           

    A) 0.25 mm

    B) 0.65 mm

    C) 1.65 mm

    D) 0.35 mm

    Correct Answer: B

    Solution :

    [b] \[\Delta L=\frac{LF}{AY},\,\,\]where \[L=3m,\] \[A=\pi {{(1.0\times {{10}^{-3}}m)}^{2}}=3.14\times {{10}^{-6}}{{m}^{2}}\] and since each wire supports one-quarter of the load, \[F=\frac{(50kg)(9.8m/{{s}^{2}})}{4}=123N\] \[\Delta L=\frac{(3m)(123N)}{(3.14\times {{10}^{-6}}{{m}^{2}})(1.8\times {{10}^{11}}N/{{m}^{2}})}\] \[=65\times {{10}^{-5}}m\,\,or\,\,0.65mm\]


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