A wire of length 5.0 m and diameter 2.0 mm extends by 0.25 mm when a force of 50 N was used to stretch it from its end. Calculate the; (a) stress on the wir...

Assessment: WAEC SSCE - Physics - 2007 (Essay) Subject: Physics

Question 1 Report

A wire of length 5.0 m and diameter 2.0 mm extends by 0.25 mm when a force of 50 N was used to stretch it from its end. Calculate the;

(a) stress on the wire;

(b) strain in, the wire. [\(\pi = 3.142\)]

Answer Details

Length \(L=5.0\,\text{m}\), diameter \(=2.0\,\text{mm}\Rightarrow r=1.0\,\text{mm}=1.0\times10^{-3}\,\text{m}\), extension \(e=0.25\,\text{mm}=0.25\times10^{-3}\,\text{m}\), force \(F=50\,\text{N}\).

(a) Stress \(=\dfrac{F}{A}\), where \(A=\pi r^2\).

\[ A=3.142\times(1.0\times10^{-3})^2=3.142\times10^{-6}\,\text{m}^2 \]\[ \text{Stress}=\frac{50}{3.142\times10^{-6}}=1.59\times10^{7}\,\text{Nm}^{-2} \]

(b) Strain \(=\dfrac{\text{extension}}{\text{original length}}\).

\[ \text{Strain}=\frac{0.25\times10^{-3}}{5.0}=5.0\times10^{-5} \]

(Strain has no unit as it is a ratio of two lengths.)

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