Power = work/time
Work = force x distance
Force = mass x acceleration
So Power = (mass x acceleration x distance) / (time)
acceleration = 8m/s / 2sec = 4 m/s²
distance = (avg speed) x (time) = 8 m
time = 2 sec
we don't know the runner's mass
Power = (mass) x (4 m/s²) x (8 m) / (2 sec)
Power = (16 x mass in kg) watts
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Slightly easier way to do it:
Power = (runner's kinetic energy at the end) / (time)
Power = (1/2 m v²) / (time)
Power = (1/2 mass) (64 m²/s²) / (2 sec)
Power = (16 x runner's mass in kg) watts
