Energy Conservation Misconception

Steps:

• Recall the law of conservation of energy: total energy in a closed system remains constant, though it can change forms.
• Evaluate A: energy transfers without loss, aligning with conservation.
• Evaluate B: inelastic collisions conserve total energy (kinetic plus thermal), despite kinetic loss.
• Evaluate C: efficiency formula is (useful output / total input) × 100%, which is standard.
• Identify D as incorrect: it claims friction reduces total energy, violating conservation.

Why D is correct:

• Friction converts mechanical energy to heat, but total energy remains constant per the first law of thermodynamics.

Why the others are wrong:

• A is correct: energy is conserved and transforms forms.
• B is correct: total energy, including non-mechanical, stays constant.
• C is correct: matches the definition of efficiency.

Final answer: D