WAEC Physics 2013 Objective — Question 14
Question 14 of 50 from the West African Examinations Council (WAEC) Physics 2013 Objective paper, with the correct answer and a full explanation.
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A body of mass 11kg is suspended from a ceiling by an aluminium wire of length 2m and diameter 2mm. Calculate the elastic energy stored in the wire [Young's modulus of aluminium = 7.0×10¹⁰Nm⁻²; g=10ms⁻², π=3.14]
- A. 1.1×10⁻¹J
- B. 5.5×10⁻²JCorrect
- C. 1.1×10⁻⁴J
- D. 5.5×10⁻⁵J
Explanation
Force on wire = weight = mg = 110N. Cross-sectional area = πd²/4 = 3.14×(2×10⁻³)²/4 = 3.14×10⁻⁶m². Extension e = Force×length/(Area×Y) = (110×2)/(3.14×10⁻⁶×7.0×10¹⁰) = 1×10⁻³m. Elastic energy E = ½Fe = ½×110×1×10⁻³ = 5.5×10⁻²J.
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