posted by Melissa on .
A 200m dash along a straight track was timed at 21.1 s by a timer located at the finish line who used the flash from the starters pistol to start the stopwatch. If the air temperature was 30.0c , what would the time have been if the timer had started the watch upon hearing the sound of the gun.
The speed of sound at that air temperature is about 345 m/s. The sound would not have arrived at the timer until 200/345 = 0.6s after the start of the race.
The recorded time would have been 20.5 s.
The delay due to the finite speed of light is negligible (about 1 microsecond).