In that universe, which objects would require quantum mechanics to describe, that is, would show both particle and wave properties?

Tell me the answers for your question and you!

If the heat engine is a perfect carnot cycle engine, thenefficiency = (t2-t1)/t2   where t1=temperature of cold reservoir ( ° k) = 135            t2=temperature of hot reservoir ( ° k)   = 325thereforeefficiency = (t2-t1)/t2 = (325-135)/325 = 0.5846 = 58%  note: this is the theoretical maximum efficiency of a perfect heat engine.   real-life engines do not achieve this value.

Decrease the surface area of the object and also decrease the concentration which will allow the particles to collide faster

Answermarble and quartzite