Several students in the group made comments to the Coach about the back pack. Which student has the correct analysis of the forces and motion of the back pack?

20%

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%