a) Distance = 2 km
1 km = 1000 m
2 km = 2 x 1000 = 2000 m
Time taken = 40 minutes
l minute = 60 seconds
40 minutes = 60 x 40 = 2400 seconds.
Speed = Distance / Time = 2000/2400 = 5/6 m/s = 0.833 m/s
b) For average speed
Total Distance covered = 2000 m + 2000 m
Total time taken = 40 min + 50 min = 90 min
= 90 x 60 s = 5400 s
Average speed = 4000/5400 s = 20/27 s = 0.74 s