Two metallic wires P and Q are made of the same material and have the same volume. Their cross-sectional areas are in the ratio 2:1. Forces F1 and F2 are applied to P and Q respectively to produce the same extension. Find F1/F2.

Correct answer: 4

Solution

Same volume: A1*L1 = A2*L2 => L1/L2 = A2/A1 = 1/2. Equal extension: F1*L1/(A1*Y) = F2*L2/(A2*Y) => F1/F2 = A1*L2/(A2*L1) = 2*2 = 4.

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