Energy dissipation via drag at terminal velocity

Steps:

• At terminal velocity, net force is zero, so acceleration is zero and speed is constant.
• Gravitational potential energy (PE) decreases as the parachutist falls.
• Kinetic energy (KE) of the parachutist remains constant due to unchanging speed.
• Lost PE is transferred to the air through drag force, converting to thermal energy via friction and turbulence.

Why B is correct:

• Drag force at terminal velocity equals gravitational force (mg = drag), dissipating mechanical energy as thermal energy in the air per the work-energy principle.

Why the others are wrong:

• A: Air gains minimal kinetic energy; drag primarily causes heating, not sustained KE.
• C: Parachutist's thermal energy increase is negligible; energy dissipates externally via air resistance.
• D: Parachutist's KE is constant at terminal velocity, so no conversion to it.

Final answer: B