We know that an object in moving with acceleration follow the rule according that
the distance covered will be : d = Vi*t + 1/2*a*t^2
where d is distance, Vi is initial speed, and a is acceleration
Then after 1 km which is 1000 metres we have:
1000 = Vi *71.2 + 1/2*0.0499*(71.2)^2
Vi = (1000-1/2*0.0499*(71.2)^2)/71.2 = 1000/71.2 - 1/2*0.0499*71.2 = 12.27 m/s
Then the car was going at 12.27 m/s when started to accelerate.
