FILE No.179Unsolved
The sky flashed, and 3 seconds later the sound of thunder was heard. Assume the light arrives instantly and the speed of sound is 340 meters per second.
About how far away is the lightning?
If you get stuck, open the hints one at a time, in order.
Which arrives first, the light or the sound?
What is the 3 seconds the time of?
Distance = speed × time.
About how far away is the lightning?
Choose the answer closest to the truth.
About 1 km
The answer is "About 1 km."
Light arrives almost instantly, so the 3 seconds is the time the sound traveled. 340 m/s × 3 s = 1,020 m, about 1 km.
About 340 m would be for 1 second, and about 10 km for 30 seconds.
Because you are not aware of the difference between light and sound.
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