Hooke's Law Ends at Proportional Limit

Steps:

• Identify the linear portion of the force-extension graph, where force is directly proportional to extension.
• Hooke's law applies only up to the proportional limit, marked by the end of the straight line.
• Beyond this, the graph curves, indicating non-proportional behavior.
• Locate the point where linearity ceases, which is option A.

Why A is correct:

• Hooke's law (F = kx) requires a straight-line graph through the origin; A marks the proportional limit where this holds.

Why the others are wrong:

• B: Lies in the elastic limit region, where extension is no longer proportional.
• C: Occurs in the plastic deformation phase, far beyond Hooke's law.
• D: Represents the breaking point, involving fracture after yielding.

Final answer: A