No heat engine can be 100% efficient because:

  1. work cannot be done
  2. energy is destroyed
  3. friction is infinite
  4. some heat must always be rejected to the cold reservoir
Answer

D) some heat must always be rejected to the cold reservoir

Second law (Kelvin statement). SLO P-11-C-13 · Knowledge

Physics MCQ · More Heat Engines, Second Law and Entropy MCQs · Practise