You are riding in an elevator on the way to the
eighteenthfloor of your dormitory. the elevator is accelerating
upwardwith a = 1.90 m/s2. beside you is the
boxcontaining your new computer; box and contents have a total
mass28.0 kg. while the elevator is accelerating upward, you
pushhorizontally on the box to slide it at constant speed toward
thedoor. if the coefficient of kinetic friction between the boxand
elevator floor is mk = 0.32, what magnitudeof
force must you apply?

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)