For the answer to the question above, the easiest way to determine is changing every runner's speed into the same unit.
First = 10 m/s
Second = 10 miles/min = 16090.34 / 60 m/s (As 1 mile = 1609.34 meter and 1 min = 60 sec)
Second = 260.82 m/s
Third = 10 cm/hr = 10*(0.01)/60*60 (As 1 cm = 0.01 m and 1 hr = 60*60 sec)
Third = 0.000028 m/s
Fourth = 10 km/sec = 10*1000 m/s (As 1 km = 1000 m and time is already in sec)
Fourth = 10000 m/s
So fastest would be the one who covers the largest distance in 1 sec. It would be the fourth one.
