Question

for which function is a heat engine most likely used?
starting an air conditioner
running a car
igniting a furnace
activating a thermostat

Explanation:

A heat engine converts heat energy into mechanical work. A car's engine (an internal - combustion engine, a type of heat engine) takes in fuel (chemical energy which is converted to heat energy during combustion) and converts it into mechanical work to move the car. An air - conditioner is a heat pump (moves heat from a low - temperature reservoir to a high - temperature reservoir, opposite of a heat engine's typical energy - conversion goal). A furnace mainly produces heat for heating a space (not focused on converting heat to mechanical work). A thermostat is a device for regulating temperature (not a heat - to - work conversion device).

Answer:

running a car