When the speed reaches 12m / s, the elevator starts to make a uniform linear motion. After 4S, the elevator stops. Calculate the height of the elevator and the average speed in the process of rising

When the speed reaches 12m / s, the elevator starts to make a uniform linear motion. After 4S, the elevator stops. Calculate the height of the elevator and the average speed in the process of rising

(1)S=gt^2=40m
(2) V ball = at = 2G * 2 = 40m / S
S Ball + 0.02 = s electricity
vt-0.5gt^2+0.02=vt+gt^2
T = root (1 / 750)