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A rod of length L , density \rho and young modulus Y is hung from the ceiling of a room . Increase in its length due to its own weigth is 

Option: 1

\frac{\rho gL^2}{2Y}


Option: 2

\frac{2Y}{\rho gL^2}


Option: 3

\frac{2\rho gL}{Y}


Option: 4

\frac{\rho^2 g^2L^2}{Y^2}


Answers (1)

best_answer

As we have learned

Elongation in terms of density -

\Delta l= \frac{MgL}{AY}

M=volume (AL)\times density (\rho )

\Delta l= \frac{\left ( AL \right )g\rho L}{AY}

\Delta l= \frac{\rho g L^{2}}{AY}
 

- wherein

\rho = density

Y =Young\: modulus

A =area\:

L =length\:

 

 Its centre of mass is at L/2 . Lets apply weight of rod at its centre of mass then elongation in its length is

 \Delta l = \frac{Mg(L/2)}{YA}= \frac{(\rho /AL)(g\frac{L}{2})}{AY}\\\\ \Delta l = \frac{\rho gL^2}{2Y}

 

Posted by

jitender.kumar

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