the time of flight of an object projected with speed 20m/s at an angle 30¡ã with the horizontal is

Answer 1

Just do the vertical part of the problem.
Vi = 20 sin30 = 10/m/s up

v = Vi - g t = 10 - 9.81 t
so t is about one second upward until v = 0 at the top.
then another second falling for a total of two seconds in the air.