You see a bolt of lightning and hear thunder two seconds later. The speed of sound is about 343 m/s. Estimate your distance from the lightning bolt.
A. 600 m
B. 1,800 m
C. 10 km
D. 40,000 km

Question

You see a bolt of lightning and hear thunder two seconds later. The speed of sound is about 343 m/s. Estimate your distance from the lightning bolt. 
A. 600 m
 B. 1,800 m
 C. 10 km 
D. 40,000 km

whpalmer4 · Answer

To work this problem, we assume that the time you see the lightning flash is the time the sound starts toward you, and that it takes no time for the light to travel the distance (at approximately 186,231 miles per second, this isn't a bad assumption!)

So, you see the flash, and two seconds later the sound waves reach your position.  Use the formula for distance:$$d = st$$where $d$ is distance, $s$ is speed, and $t$ is time.  Your answer won't be exactly one of the choices, but it should be much closer than any of the other choices.  The problem does say to estimate...

anonymous · Answer

ok so it would be closest to 600m since 343 * 2 is 686

whpalmer4 · Answer

Yep!  Another rule of thumb is that every 5 seconds is about a mile.  Closer to 4.7 seconds, really.

anonymous · Answer

Ok! thanks so much :)