Question

If you see a lightning stroke and then, 15 seconds later, hear the thunder, the lightning is about ____ miles away

Answer 1

Answer:

3.2 miles

Explanation:

We can assume that the light coming from the lightning reach instantaneously our eyes (because light travels very fast, $3\cdot 10^8 m/s$), so the time between the lightining and the hearing of the thunder is equal to the time that sound takes to each us.

Sound travels in air approximately at speed

v = 343 m/s

So the distance it covers in a time of t = 15 seconds is

$d=vt=(3403 m/s)(15 s)=5145 m$

And using the conversion from meters to miles,

1 mile = 1609 meters

we find

$d=\frac{5145 m}{1609 m/miles} = 3.2 miles$