Let's say you throw a projectile with initial velocity v at an angle. I assign the velocity as positive, displacement in air as positive and acceeration as negative. What about after the apex when v = 0? Does velocity then become a negative value and g stay the same for in the kinematics equations?

I ask because of this question

"Q: What is the range for a projectile launched at 45 deg angle that has a flight time of 3 seconds?

A. 14.2m

B. 44.1m

C. 72.2m

D. 144.4m

the berkley review "turbo-solution" is

With a flight time of 3 seconds, it takes 1.5 seconds to reach its apex. A 1 second drop time covers 5m and a 2-second drop time covers 20m, so a 1.5 second drop covers about 11 to 12m, so the max height is about 11-12m. The range for a 45 deg launch is four times the max height so R ~ 44-48 m."

i see you can use y = 1/2at^2 to obtain 11-12, but why is a positive? Isn't gravity working opposite displacement and thus would be negative? Thanks.