Which expression shows conservation of energy in an engine's energy transformation?

• A. Mechanical = chemical
• B. Chemical = mechanical + sound + heat
• C. Chemical + mechanical = sound + heat
• D. Sound = heat

Answer: (B)

In an engine, energy must be conserved: the chemical energy stored in the fuel is transformed into other forms, including the useful mechanical work and various losses. The best expression captures this by saying the chemical energy equals the mechanical energy produced plus the energy lost as sound and as heat. This shows the total energy coming from the fuel is accounted for in the outputs.

Why this fits: it reflects the real process where fuel’s chemical energy is converted into motion (work) and dissipated energy (heat from inefficiencies, and sound from moving parts). The equation is bookkeeping: all the chemical energy input ends up as mechanical energy plus waste energy.

Why the other forms don’t fit: pairing only mechanical with chemical ignores losses; energy isn’t all mechanical—there’s always heat and sound as some of the fuel’s energy is wasted. Treating energy as if sound and heat stand alone or as equal to heat without referencing the chemical source also misstates where the energy comes from and where it goes.