Energy balance at terminal velocity Steps:

• Terminal velocity means drag force equals gravitational force, resulting in zero net force and constant speed.
• Gravitational potential energy (PE = mgh) decreases as the parachutist descends.
• This lost PE is transferred via drag to the air, primarily as kinetic energy to air molecules.
• The kinetic energy in the air eventually dissipates to thermal energy, but the direct conversion is kinetic, not thermal.

Why B is correct:

• Air resistance imparts kinetic energy to the air (per work-energy theorem, work by drag = change in air's KE); thermal energy arises secondarily from viscous dissipation, not directly from PE.

Why the others are wrong:

• A: Correct, as drag directly accelerates air, increasing its kinetic energy.
• C: Correct, friction between parachute/body and air generates some heat in the parachutist.
• D: Correct, constant velocity means constant kinetic energy (½mv²) for the parachutist.

Final answer: B