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A steel rod used in construction has a radius of 10 mm and a length of 1.0 m. It is pulled by a force of 100 kN. Taking Young’s modulus of structural steel as 2 × 10¹¹ N m⁻², the approximate percentage strain in the rod is

1. 0.16%
2. 0.32%
3. 0.08%
4. 0.24%

Correct answer: 0.16%

Solution

A = pi*r^2 = pi*(0.01)^2 = pi*10^-4 m^2. Strain = F/(A*Y) = 10^5/((pi*10^-4)*(2*10^11)) = 1/(2*pi*100) = 1.59*10^-3, i.e. about 0.16%.

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