Misconception on energy conservation in machines

Steps:

• Recall the law of conservation of energy: energy transforms but total amount remains constant.
• Evaluate each statement against this law and related principles like collisions and efficiency.
• Identify friction's role: it dissipates energy as heat, but total energy is still conserved.
• Confirm D violates conservation by implying energy loss rather than transformation.

Why D is correct:

• Friction converts mechanical energy to thermal energy, but total energy remains constant per the first law of thermodynamics; it does not reduce total energy.

Why the others are wrong:

• A: Correctly states the conservation of energy, where energy transfers forms but is never lost.
• B: In elastic collisions, both kinetic energy and momentum are conserved, keeping total energy constant.
• C: Matches the standard definition of efficiency as useful output over total input energy.

Final answer: D