kinematics

[red and white kop!]

a car comes to a stop from a speed of 30m/s in a distance of 804m. the driver brakes so as to produce a deceleration of 1/2 m/s/s to begin with, then brakes harder to produce a deceleration of 3/2 m/s/s. Find the speed of the car at the instant the decelaration is increased, and the total time it takes for the car to stop.

i've toiled over this for a whole day. im sure there's something im missing! i dont understand how i can get v without t! so i drew up a graph and tried to combine all these equations but there are just too many unknowns for me! can someone help me solve this step by step?

 

[Aladdin]

Use V=u^2+2ax

Set the first equation for the first interval , and another equation for the second interval .