A force of 40 N is applied at the end of a wire 4m long and produces an extension of 0.24mm. If the diameter of the wire is 2.00mm, calculate the; (i) stres...

Assessment: WAEC SSCE - Physics - 2000 (Essay) Subject: Physics

Question 1 Report

A force of 40 N is applied at the end of a wire 4m long and produces an extension of 0.24mm. If the diameter of the wire is 2.00mm, calculate the;

(i) stress on the wire; (ii) strain in the wire.

Answer Details

A force \(F = 40\,\text{N}\) stretches a wire of length \(L = 4\,\text{m}\), producing an extension \(e = 0.24\,\text{mm} = 0.24\times10^{-3}\,\text{m}\); the wire diameter is \(2.00\,\text{mm}\), so radius \(r = 1.00\times10^{-3}\,\text{m}\).

Cross-sectional area:

\[ A = \pi r^{2} = 3.142\times(1.00\times10^{-3})^{2} = 3.142\times10^{-6}\,\text{m}^{2} \]

(i) Stress on the wire:

\[ \text{stress} = \frac{F}{A} = \frac{40}{3.142\times10^{-6}} = 1.27\times10^{7}\,\text{Nm}^{-2} \]

(ii) Strain in the wire:

\[ \text{strain} = \frac{e}{L} = \frac{0.24\times10^{-3}}{4} = 6.0\times10^{-5} \]

(Strain is a ratio and has no unit.)

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