Select all the correct answers. Which two statements are true about a system?

- A system is a group of objects analyzed as one unit.
- Energy that moves across system boundaries is conserved. - There's only one way to define the boundaries of a system.
- All systems are made by humans.​

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)

Friction removes energy from objects in motion. which statement best describes how this works? a) friction transforms ke into thermal energy b) friction transfers thermal energy to ke c) friction transforms te into pe d) friction transforms pe into ke e) friction transfers ke into pe

Formulating a hypothesis: part i since the investigative question has two variables, you need to focus on each one separately. thinking only about the first part of the question, mass, what might be a hypothesis that would illustrate the relationship between mass and kinetic energy? use the format of " because when writing your hypothesis