Energy Transformation in Bungee Jumping

Steps:

• Identify energies: gravitational PE (mgh), kinetic KE (1/2mv²), elastic PE (1/2kx²).
• Platform (A): only GPE non-zero; KE and elastic PE are zero.
• Free fall (B): GPE and KE non-zero; elastic PE zero as cord slack.
• Cord stretch to bottom (C): GPE decreases but non-zero, KE from motion non-zero until stop, elastic PE builds as cord extends.
• At stationary bottom: KE zero, but prior instant during descent all three present.

Why C is correct:

• During cord extension to bottom, total energy E = mgh + 1/2mv² + 1/2kx², all terms non-zero by conservation of energy before KE reaches zero.

Why the others are wrong:

• A: Elastic PE zero (cord not stretched); KE zero (at rest).
• B: Elastic PE zero (cord not yet extending).

Final answer: C