First slide

Elastic behaviour of solids

Question

Steel and copper wires of same length are stretched by the same weight one after the other. Young's modulus of steel and copper are $2 \times 10^{11} N / m^{2}$ and $1 .2 \times 10^{11} N / m^{2}$ . The ratio of increase in length

Moderate

A

$\frac{2}{5}$
B

$\frac{3}{5}$
C

$\frac{5}{4}$
D

$\frac{5}{2}$

Solution

$\begin{array}{l} l = \frac{FL}{AY} \Rightarrow \frac{l_{S}}{l_{cu}} = \frac{Y_{cu}}{Y_{S}} (\underline{\underline{F}} \underline{L} and Y are constant) \\ ∴ \frac{l_{s}}{l_{cu}} = \frac{1 .2 \times 10^{11}}{2 \times 10^{11}} = \frac{3}{5} \end{array}$

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