Which statement explains the flow of heat? Heat moves from one place to another like a radiating wave. Heat moves as packets of energy are transferred from one substance to another. Heat moves as molecules of one substance collide with molecules of another substance, transferring kinetic energy.

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.