Aheat engine takes in 840 kj per cycle from a heat reservoir. which is not a possible value of the engine's heat output per cycle?

We have by the first law of thermodynamics tha energy is preserved, hence we cannot have over 840kJ per cycle. We have by the laws of thermodynamics (the 2nd one in specific) that the entropy of a system cannot increase. We cannot have an output of  840 kJ per cycle from a heat engine because then that would mean that the entropy would stay the same, while any heat engine increases it. Hence, any value is acceptable.

therefore, the efficiency is:

1) when you rub your hands together quickly, the kinetic energy is converted to mechanical energy.2) thermal energy from the sun travels to earth as infrared waves.3) energy is transferred through the matter of space by electromagnetic waves. 4) when a match is burned, chemical potential energy is converted to thermal and radiant energy. 5) seismicwaves are caused by back and forth movement , or vibration, of an object. 6) mechanicalenergy in an engine changes thermal energy into kinetic energy to make a car move.