An 90 kg man stands in an elevator. What force does the floor of the elevator exert on the man if, the elevator is stationary? b) the elevator accelerates upward at 1.2 m/s2? c) the elevator rises with constant velocity 3 m/s? d) while rising, the elevator decelerates at 0.5 m/s2? e) the elevator descends with constant velocity of 2.5 m/s