A model rocket blasts off and moves upward with an acceleration of 12m/s^2 until it reaches a height of 30m , at which point its engine shuts off and it continues its flight in free fall.
A-what is max height?
B-What is speed just before the rocket hits the ground?
C-What is rockets total duration of flight?

To figure the speed of the rocket when it reaches 30m you need to use the sqrt(2*12m/s/s*30m)

and after that it will slow down at -9.8m/s/s

thus reverse the above eqn for distance and use 9.8 (it will be the same, you can't have a negative distance) for acceleration.

(2*[speed at 30m]^2)/9.8 will give you the distance it travels after 30m.

total distance = 30m + distance after 30m

sqrt(2*9.8*[total distance]) speed at grnd

I can't think of the time eqn... too late for me... good luck.