Which of the following is an example of the law of conservation of energy?
a. electrical energy transforming into sound energy in a speaker
b. running out of energy after exercising for a long time
c. running out of gas in a car
d. turning lights off when you aren’t using them

Air is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. air enters the heat exchanger at 95 kpa and 20°c at a rate of 0.6 m^3/s. the combustion gases (cp = 1.10 kj/kg°c) enter at 160°c at a rate of 0.95 kg/s and leave at 95°c. determine the rate of heat transfer to the air and its outlet temperature.