Answer:
(a) The second wire will be stretched by 2 mm
(b) The third wire will be stretched by 0.25 mm
Explanation:
Tensile stress on every engineering material is given as the ratio of applied force to unit area of the material.
σ = F / A
Tensile strain on every engineering material is given as the ratio of extension of the material to the original length
δ = e / L
The ratio of tensile stress to tensile strain is known as Young's modulus of the material.

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<u>Part A</u>
cross sectional area and applied force are the same as the original but the length is doubled

The second wire will be stretched by 2 mm
<u>Part B</u>
a third wire with the same length but twice the diameter of the first

e₁ = ¹/₄ x 1 mm = 0.25 mm
The third wire will be stretched by 0.25 mm