Step-by-step explanation:
Initial vertical velocity = 10 m/s sin 30
then gravity starts to slow it down:
v= 10 sin 30 - a t where a = 9.81 m/s^2
v = 10 sin 30 - 9.81 t when velocity = 0 the ball starts back down and takes the same amount of time to come back down from this height
0 = 10 sin30 - 9.81 t shows t = .509 s
Double this for the time when it has come back down and hits the ground = 1.02 s