JEE Main & Advanced JEE Main Paper (Held On 10 April 2016)

  • question_answer
    A thin 1m long rod has a radius of 5 mm. A force of \[50\,\,\pi kN\]is applied at one end to determine its Young's modulus. Assume that the force is exactly known. If the least count in the measurement of all lengths is 0.01 mm, which of the following statements is false?   JEE Main Online Paper (Held On 10 April 2016)

    A) The maximum value of Y that can be determined is \[{{10}^{14}}N/{{m}^{2}}\]

    B) \[\frac{\Delta Y}{Y}\]?gets minimum contribution from the uncertainty in the length.

    C) The figure of merit is the larges for the length of the rod.

    D) \[\frac{\Delta Y}{Y}\]gets its maximum contribution from the uncertainty in strain.

    Correct Answer: A

    Solution :

                 \[\ell =1m\]              \[r=5\times {{10}^{-3}}m\]              \[F=50\pi \,\times {{10}^{3}}N\]                \[\gamma =\frac{F/A}{\frac{\Delta \ell }{\ell }}\]              \[\gamma =\frac{\Delta \ell }{\ell }=\frac{F}{A}\]              \[\gamma =\frac{50\pi \times {{10}^{3}}}{\pi \times {{(5\times {{10}^{-3}})}^{2}}}\times \frac{\ell }{\Delta \ell }\]              \[\gamma =\frac{50\times {{10}^{3}}}{25\times {{10}^{-6}}}\times \frac{1}{\Delta \ell }\Rightarrow \gamma =\frac{2\times {{10}^{9}}}{\Delta \ell }\]              \[\gamma =\frac{2\times {{10}^{9}}}{\varepsilon }\] \[\gamma \max .=2\times {{10}^{9}}\]


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