You hear thunder 5 seconds after seeing the lightning flash. Approximately how far away did the lightning strike? (Use speed of sound in air ≈ 340 m/s; speed of light is effectively instantaneous over this range.)
A1700 m
B3400 m
C850 m
D170 m
Answer & Solution
Correct answer: A. 1700 m
Light reaches you almost instantly. Sound takes 5 s. Distance = speed × time = 340 m/s × 5 s = 1700 m. So the lightning struck about 1.7 km away. This is the basis of the 'count seconds between flash and thunder' rule of thumb to estimate storm distance.
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