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A steel wire and a copper wire of equal cross-sectional area are joined end to end and put under tension. The extensions in the two wires are observed to be equal. Find the ratio of length of steel wire to copper wire. (Young's modulus: steel = 2.0 x 10¹¹ N/m², copper = 1.1 x 10¹¹ N/m².)

1. 2: 1
2. 20: 11
3. 1: 1
4. 11: 20

Correct answer: 20: 11

Solution

With equal force, area, and extension, L is proportional to Y, so L_steel: L_copper = Y_steel: Y_copper = 20: 11.

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