When timing the 100-m run, officials at the finish line are instructed to start their stop-watches at the sight of smoke from the starter's pistol and not on the sound of its firing. Explain. What would happen to the times for runners if the timing started when sound was heard

It would arrive 0.29 seconds later

Step-by-step explanation:

The first thing to keep in mind is that light travels at 3.00 x 10 ^ 8 m / s and sound travels at 343 m / s.

Being 100 meters the race would be:

100 m / 343 m / s = 0.29 s.

Therefore, The sound would arrive at the finish line around a third of a second after the runner had started. Therefore a time would be around a third of second too short.