Question

A rifle is fired in a valley with parallel vertical walls. The echo from one wall is heard 1.0s after the rifle was fired. The echo from the other wall is heard 1.0s after the first echo. How wide is the valley?

Answer 1

Look up the speed of sound at the conditions in the valley. At sea level I found about 340 m/s but use the speed you find.
It took 1.0 sec for the echo from the first wall which means the distance from the rifle to the first wall is 340 m/s * 1 sec * 1/2 = ?? (the sound had to travel there AND back. The distance from the rifle to the second wall was
340 m/s * 2 sec * 1/2 = ??
Add the two together to obtain the distance between the two walls. Check my thinking.

Answer 2

Yes, I am supposed to use 343 m/s so:

(343)(1)(.5)+(343)(2)(.5)=514.5 m/s

Answer 3

Looks ok to me. However, if your prof is concerned about significant figures, (some are, some aren't), you have only two with 1.0 seconds so you need to round the answer.