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A wire stretches by 1.0 mm when a load W hangs from it. The same wire is now passed over a frictionless pulley and a weight W is hung from each of its two ends. What is the elongation of the wire now?

1. 0.5 mm
2. 1.0 mm
3. 2.0 mm
4. 4.0 mm

Correct answer: 1.0 mm

Solution

Tension in the wire is W in both situations (the wall in case 1 supplies a reaction W, just like the second weight in case 2), so elongation is unchanged at 1.0 mm.

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