Aball is thrown upward from the ground with an initial speed of 15.6 m/s; at the same instant, another ball is dropped from a building 20 m high. after how long will the balls be at the same height above the ground?

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.