let each runner starts from rest
v₀ = initial velocity of each runner = 0 m/s 
t = time of travel = 2 sec = 
a = average acceleration
average acceleration is given as 
a = (v - v₀)/t
inserting the values
a = (v - 0)/t
a = v/t 
since each runner gains equal amount of speed in given time interval of "t". hence the average acceleration of each runner is same.