Work = Force × distance
We need to calculate distance travelled.
20km/hr = 20,000m / 60min → 333.3m/ min
333.3 × 3.5 min = 1,166.6 meters travelled
Force = 700 N and distance = 1,166.6 m
Work done is 700 N × 1,666.6 = 816,620 Nm
Power output = work /time
Power output is 816, 620 Nm / (3.5 × 60sec) →816, 620 / 210 = 3,888.7
Power output is 3,888.7 Watts.
Power output can also be expressed in joules per second so it is also correct to say work done is 3,888.7 J/s