you are designing a high speed elevator for a new skyscraper. the elevator has a mass of 2400kg. for passenger comfort you choose the maximum ascent speed to be 18m/s. the maximum descent speed to be 10.0 m/s and the max acceleration magnitude to be 5.40 m/s 2 . what is the minimun time it will take the elevator to ascend from the lobby to the observation deck a vertical displacement of 640 m