WAEC Physics 2021 Theory — Question 12
Question 12 of 35 from the West African Examinations Council (WAEC) Physics 2021 Theory paper, with the correct answer and a full explanation.
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8(a)(ii). A spring has a length of 0.20 m when a mass of 0.30 kg hangs on it, and a length of 0.75 m when a mass of 1.95 kg hangs on it. Calculate the: I. force constant of the spring; II. length of the spring when unloaded. [g=10 ms⁻²]
Model answer
Weights: F1=0.30×10=3N, F2=1.95×10=19.5N. Using F=k×extension: 3=k(0.20-l₀) and 19.5=k(0.75-l₀). Dividing and solving simultaneously gives k=30 Nm⁻¹ and unloaded length l₀=0.10 m.
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