Cars are inefficient by the fact that they convert fuel (chemical energy) to mechanical energy, only 30-40% of that energy can be converted to move the car.
Since Thermodynamic is basically about the conversion of energy, cars are inefficient since something has to be able to convert at least 50-75% of the energy to be efficient.
Cars are the mechanical device which convert chemical energy of fuel into mechanical energy, the engine used in the automobiles car are very inefficient, they can only convert 30-40% of chemical energy of fuel into mechanical energy, since thermodynamics is the branch of science that deals with the conversion of energy, thus due to poor conversion rate of chemical energy into mechanical energy, cars are known as inefficient machine.
