A load-extension graph for a spring is displayed. Which point marks the limit of proportionality for the spring, and what is the spring constant of the spring equal to?
- Alimit of proportionality: Q, spring constant is equal to the gradient of PQ
- Blimit of proportionality: Q, spring constant is equal to the gradient of QR
- Climit of proportionality: R, spring constant is equal to the gradient of PQ
- Dlimit of proportionality: R, spring constant is equal to the gradient of QR