Answer:
12.5 m/s
Explanation:
If the avg speed is 10 m/s we assume that the speed is constant and not fluctuating
If VT (Velocity*Time) is equal to speed at the end of the 4 seconds of accel. it is the top speed at the finish line
since the speed is 0 at the beginning of races, we will use V0= 0 m/s
So the avg velocity for those 4 seconds is (VT+V0) /2 = or 1/2 VT (for 40% of the race)
The avg velocity for the last 6 seconds is, of course, VT (for 60% of the race
hence
(1/2VT)(.4) + VT(.6) = 10 m/s
VT = 10/.8 = 12.5 m/s
