Answer:
b. 20%
Step-by-step explanation:
Efficiency of an engine is a ratio in percentage of the work done to the energy intake of the engine.
η=(Q₁-Q₂)/Q₁×100%
η is efficiency, Q₁ is the energy intake, Q₂ is energy wasted.
The information provided is:
Energy intake = 400 J
Work done = 80 J = (400-320) =Q₁-Q₂
Energy wasted =320 J
η= 80/400×100%
=20%