JAMB Physics 2017 Paper

Concept:Hooke's Law states that extension is directly proportional to the applied force, $F = ke$, where $k$ is the force constant.Explanation:First, find the force produced by the suspended load: $F = mg = 0.8 \times 10 = 8\,\text{N}$.Using Hooke's Law for the first case: $8 = k \times 0.04$.So the force constant is $k = \frac{8}{0.04} = 200\,\text{N/m}$.The same spring keeps the same value of $k$.For the second case, $F = 16\,\text{N}$, so $16 = 200 \times e$.Therefore, the new extension is $e = \frac{16}{200} = 0.08\,\text{m}$.Answer:The string will extend by $0.08\,\text{m}$.Correct option: D. $0.08\,\text{m}$.