The mechanical energy of a football during a pass is

a. potential energy
b. kinetic energy
c. gravitational potential energy
d. potential and kinetic energy

The answer is D because the football starts out with potential but changes to kinetic midair, then back to potential.

The answer would be a

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.