First slide

Elastic behaviour of solids

Question

Young's modulus of rubber is $10^{4} N / m^{2}$ and area of cross-section is $2 {cm}^{2}$ . If force of $2 \times 10^{5}$ dynes is applied along its length, then its initial length l becomes

Moderate

A

3L
B

4L
C

2L
D

None of the above

Solution

$\begin{array}{l} Y = 10^{4} N / m^{2}, A = 2 \times 10^{- 4} m^{2}, F = 2 \times 10^{5} dyne = 2 N \\ l = \frac{FL}{AY} = \frac{2 \times L}{2 \times 10^{- 4} \times 10^{4}} = L \end{array}$
$∴$ Final length = initial length + increment = 2L

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