WAEC Physics 2017 Theory — Question 4
Question 4 of 33 from the West African Examinations Council (WAEC) Physics 2017 Theory paper, with the correct answer and a full explanation.
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4. A spiral has a length of 14cm when a force of 4N is hung on it. A force of 6N extends the springs by 4cm. Calculate the unstretched length of the spring.
Model answer
l0 = original length of spring, e = extension. Given: l0+e1=14cm, e1=14-l0; and second case e2=4cm with f1=4N, f2=6N. Since f=ke, k=f/e = constant: f1/e1=f2/e2 → 4/(14-l0)=6/4. Solving: 4x4=6x(14-l0) → 16=84-6l0 → 6l0=84-16=68 → l0=68/6=11.33cm.
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