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NEET2018PhysicsMechanical Properties of SolidsActual

Two wires are made of the same material and have the same volume. The first wire has cross-sectional area A and the second wire has cross-sectional area 3 A . If the length of the first wire is increased by ∆ l on applying a force F , how much force is needed to stretch the second wire by the same amount?

Options

  1. A4 F
  2. B6 F
  3. C9 F
  4. DF

Correct answer

C. 9 F

Step-by-step solution

Y = F l A ∆ l ∵     V = A l   s o   l = V A F = Y A ∆ l l = Y A 2 ∆ l V F 1 F 2 = A 1 A 2 2 ⇒ F F 2 = A 3 A 2 = 1 9 F 2 = 9 F 1 = 9 F

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