Practice question · Multiple choice
A regenerative braking system recovers perhaps 70% of a vehicle's kinetic energy, never 100%. Which law sets the ceiling?
Hints
- Ask where the missing 30% goes, and whether it could be gathered back.
- Energy is conserved. So what exactly is being lost?
Show the answer
C. The second law, since every conversion disperses some heat
Why
No energy is destroyed, the first law forbids that, and some is converted to heat spread across the motor, wiring and air, which cannot be reassembled into motion without further loss. Efficiency is bounded by the second law, so 70% is close to the practical ceiling rather than a failure of engineering.
Practise Work, Energy, and Power
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