According to newton's law of cooling, if a body with temperature upper t 1 is placed in surroundings with temperature upper t 0, different from that of upper t 1, the body will either cool or warm to temperature t(t) after t minutes, where t(t)equalsupper t 0plus(upper t 1minusupper t 0)e superscript negative kt. a cup of coffee with temperature 140degreesf is placed in a freezer with temperature 0degreesf. after 15 minutes, the temperature of the coffee is 41degreesf. use newton's law of cooling to find the coffee's temperature after 20 minutes.

Air enters a gas turbine with two stages of compression and two stages of expansion at 100 kpa and 17°c. this system uses a regenerator as well as reheating and intercooling – the intercooler returns the air to the inlet temperature. the pressure ratio across each compressor is 4 ; 300 kj/kg of heat are added to the air in each combustion chamber; and the regenerator operates perfectly while increasing the temperature of the cold air by 20°c. determine the system’s thermal efficiency. assume isentropic operations for all compressor and the turbine stages and use constant specific heats at room temperature. (0.378)