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Comments (2)
Goh Ying Ting said
at 10:03 pm on Feb 19, 2014
Hi Mr Ang, could you help me with this question please? Thank you!:)
The time keeper in a 100m race in a school sport starts the stopwatch after hearing the shot from the starter pistol. Will the time recorded be shorter or longer than the actual time and by how much?
johnlittlephysics said
at 1:53 am on Feb 21, 2014
The starter pistol is at the start point. We assume the time keeper is at the end point, 100 m away. The time keeper would only start the time after the sound has travelled 100 m to her. So she would have started the stopwatch after the runner has already started running. The time recorded by her would be shorter than the actual time by t = 100 m / speed of sound in air.
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