Since the acceleration of the car is constant, the car is moving by uniformly accelerated motion, and the velocity of the car at time t can be written as
[tex]v(t) = v_0 + at[/tex]
where [tex]v_0 = 25 m/s[/tex] is the initial velocity of the car
a is the acceleration
t is the time
At time [tex]t = 6 s[/tex], the velocity of the car is zero: [tex]v(t)=0[/tex], so we can re-arrange the previous formula to get the acceleration of the car
[tex]a=- \frac{v_0}{t}=- \frac{25 m/s}{6 m/s}=-4.17 m/s^2 [/tex]
and the negative sign means the direction of the acceleration is against the direction of motion of the car (in fact, the car is decelerating).
