Answer: He would reach 7m/s at the distance of 17,5m.
Explanation: In order for us to know how long it takes for the speed to be reached, we use the equation V= Vo + at, with V=7m/s, Vo= 0m/s since you start from rest and a=1.4m/s². T is the time in seconds that we want to find out.
7 = 0 + 1.4t
7 = 1.4t
t= 5s
Now, we want to know the distance this boy reaches in 5 seconds, in a 7m/s speed and accelarating in 1.4m/s². For finding this out, we use another equation, S = So + Vot + (at²)/2, S being the final distance, So = 0m because he started from rest, and the other variables used before.
S = 0 + 0*5 + [1.4*(5²)]/2
S = 0 + 0 + (1.4*25)/2
S = 35/2
S = 17,5m
