Force-extension graph regions and energy absorption

Steps:

• Elastic region is linear from origin, obeying Hooke's law (stress proportional to strain).
• Plastic region follows yield point, showing nonlinear extension with permanent deformation.
• Work done to break is total area under force-extension curve, representing energy absorbed.
• Correct graph labels elastic as initial slope, plastic as curved section, and shades full area under curve.

Why D is correct:

• D accurately shows elastic as linear segment, plastic as post-yield curve, and full shaded area as work done per work-energy principle (W = ∫F dx).

Why the others are wrong:

• A mislabels plastic as linear part, ignoring permanent deformation.
• B shades only elastic area, underestimating total work to fracture.
• C swaps elastic and plastic regions, violating Hooke's law.

Final answer: D