Consider a cylindrical nickel wire 1.6 mm in diameter and 2.5 × 104 mm long. Calculate its elongation when a load of 320 N is applied. Assume that the deformation is totally elastic and that the elastic modulus for nickel is 207 GPa (or 207 × 109 N/m2).

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Answer:

0.192 m

Explanation:

The young's modulus of the Nickel wire is given as,

γ = Stress/Strain

γ = (F/A)/ΔL/L

γ = FL/ΑΔL.................... Equation 1

Where γ = young's modulus of the Nickel wire, F = Load applied, A = cross sectional area of the nickel wire, L = Length of the nickel wire, ΔL = Elongation.

make ΔL the subject of the equation

ΔL = FL/γA..................... Equation 2

Also,

A = πd²/4................ Equation 3

d = diameter of the of the wire

Substitute equation 3 into equation 2

ΔL = 4FL/γπd²............... Equation 4

Given; F = 320 N, L = 2.5×10⁴ mm = 250 m, d = 1.6 mm = 0.0016 m, γ = 207×10⁹ N/m², π = 3.14

Substitute into equation 4

ΔL = (4×320×250)/(207×10⁹×3.14×0.0016²)

ΔL = 320000/1663948.8

ΔL = 0.192 m

When a load of 320 N is applied, its elongation would be "21.113 mm".

Elastic modulus

According to the question,

Length of wire = 16 mm

Force = 320 N

Young's modulus (E) = 207 GPa or,

                                  = 207 × 10³ MPa

Now,

The stress developed in wire will be:

→ σ = [tex]\frac{P}{A}[/tex]

By substituting the values,

      = [tex]\frac{320}{\frac{\pi}{4}\times (1.7)^2 }[/tex]

      = 140.98 MPa

The strain will be:

→ [tex]\epsilon[/tex] = [tex]\frac{\sigma}{E}[/tex]

     = [tex]\frac{140.98}{207\times 10^3}[/tex]

     = 6.811 × 10⁻⁴

hence,

Total deformation will be:

= Elastic strain × Total length

= 6.811 × 10⁻⁴ × 3.1 × 10⁴

= 21.113 mm

Thus the above answer is correct.

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