Identical springs of steel and copper are equally stretched. On which, more work will have to be done?


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Work done in stretching a wire, W = \(\frac{1}{2}\)Fx∆l.

[F = applied force, ∆l = extension in wire]

Spring are equally stretched, therefore, for same force (F).

W ∝ ∆l (i)

Y(Young’s modulus)

Y = \(\frac{F}{A}\) × \(\frac{l}{∆l}\) or ∆l = \(\frac{F}{A}\) × \(\frac{l}{Y}\)

Both springs are identical

∆l ∝ \(\frac{l}{Y}\) (ii)

From (i) & (ii)

W ∝ \(\frac{l}{W}\) or \(\frac{Y_{steel}}{W_{copper}}\) = \(\frac{Y_{copper}}{Y_{steel}}\) < 1 (∴ Ysteel > Ycopper)

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