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The elastic potential energy stored in a steel wire of length 20 m stretched through 2 cm is 80 J. The cross sectional area of the wire is ______ mm². (Given, y = 2.0 × 10¹¹ N m⁻²)

1. 40
2. 40
3. 40
4. 40

Correct answer: 40

Solution

The elastic potential energy stored in a stretched wire can be calculated using the formula U = (1/2) * (F² / y * A), where F is the force applied, y is Young's modulus, and A is the cross-sectional area. Given the values, the calculations confirm that the cross-sectional area of the wire is indeed 40 mm².

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