WAEC Physics 2010 Theory — Question 2
Question 2 of 22 from the West African Examinations Council (WAEC) Physics 2010 Theory paper, with the correct answer and a full explanation.
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2. A force of 40 N is applied at one end of a wire fixed at one end to produce an extension of 0.24 mm. If the original length and diameter of the wire are 3 m and 2.0 mm respectively, calculate the (a) stress on the wire (b) strain in the wire.
Model answer
Given: Force (F)=40N, extension (e)=2.4x10⁻⁴m, original length=3m, diameter (d)=2.0mm=2x10⁻³m. (a) Area = πd²/4 = π(2x10⁻³)²/4. Stress on the wire = Force/Area of wire = 40/(3.14x(2x10⁻³)²/4) = 40/(3.14x4x10⁻⁶/4) = 1.27x10⁷ N/m². (b) Strain in the wire = Extension/original length = 2.4x10⁻⁴/3 = 8x10⁻⁵.
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