Answer:
Part 1) Speed at s = 420 meters =12.26 m/s
Part 2) Time required to cover the distance = 26 seconds
Step-by-step explanation:
This problem can be solved using third equation of kinematics as follows

where
'v' is the final velocity
'u' is the initial velocity
'a' is the acceleration of the car
's' is the distance covered between change in velocities
Now during the time at which the car moves it cover's a distance of 420 m-100 m=320 meters
Thus applying values in the above equation we get

The time to reach this velocity can be found using first equation of kinematics as
