Answer
31.8 m/s
Work Step by Step
The car which is at rest accelerates until $\frac{1}{4}$ of the distance is covered and then retards until it becomes to rest. Therefore, the car attains maximum speed when it just covers $\frac{1}{4}$ of the distance.
With the help of the kinematic equation $v=u+at$,
we can find the maximum speed.
Initial velocity u=0
Acceleration a= $2.25\,m/s^{2}$ and
time taken t= 14.14 s (obtained in the previous part)
Therefore, $v=2.25\,m/s^{2}\times14.14\,s=31.8\,m/s$
