Question

Sound travels at a speed of about 340m/s in the air. How long will it take an explosion to be heard from a distance of 20 miles away ?

Answer 1

First convert the speed of sound from meters/second to miles/second:

$340\,\dfrac{\mathrm m}{\mathrm s}\cdot\dfrac{3.281\,\mathrm{ft}}{1\,\mathrm m}\cdot\dfrac{1\,\mathrm{mi}}{5280\,\mathrm{ft}}=0.21\,\dfrac{\mathrm{mi}}{\mathrm s}$

Then the time it takes for the sound to travel 20 miles is

$\dfrac{20\,\mathrm{mi}}{0.21\,\frac{\mathrm{mi}}{\mathrm s}}=95\,\mathrm s$