Stress and strain — practice question

The graph illustrates how the length of a spring changes when a larger load is applied and it is stretched. What is the spring constant?

• A$8.0\,\text{N m}^{-1}$
• B$2.7\,\text{N m}^{-1}$
• C$0.13\,\text{N m}^{-1}$
• D$0.080\,\text{N m}^{-1}$