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QTest #9-solutions

# QTest #9-solutions - Version 126/ABDDC QTest#9...

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Version 126/ABDDC – QTest #9 – Antoniewicz – (57420) 1 This print-out should have 4 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points Two wires made of the same material are stretched by equal forces. The second wire is twice as long as the first one and also has twice the diameter of the first wire. If the first wire is stretched by 5 . 2 cm , then by how long is the second wire stretched? 1. 4.05 2. 2.6 3. 0.7 4. 4.5 5. 3.5 6. 4.1 7. 1.65 8. 2.0 9. 3.25 10. 3.45 Correct answer: 2 . 6 cm. Explanation: Let : Δ L 1 = 5 . 2 cm , L 2 = 2 L 1 , and r 2 = 2 r 1 . Young’s modulus is Y = F L A Δ L = F L π r 2 Δ L Y F = L π r 2 Δ L . The forces are the same, so L 1 π r 2 1 Δ L 1 = L 2 π r 2 2 Δ L 2 Δ L 2 = L 2 L 1 parenleftbigg r 1 r 2 parenrightbigg 2 Δ L 1 = 2 parenleftbigg 1 2 parenrightbigg 2 Δ L 1 = 1 2 Δ L 1 = 1 2 (5 . 2 cm) = 2 . 6 cm . 002(part1of2)5.0points Consider the 81 N weight held by two cables shown below. The left-hand cable is horizon- tal.

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QTest #9-solutions - Version 126/ABDDC QTest#9...

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