A person, with his ear to the ground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 0.80 s apart. How far away did the impact occur? The speed of sound in air is 343 m/s, and in concrete is 3000 m/s.

309 m

Explanation:

time apart = 0.8 s

speed of sound in air = 343 m/s

speed of sound in concrete = 3000 m/s

lets assume it time it takes to travel trough concrete = T

the time it takes to travel through air = T + 0.8 since they are 0.8 s apart

the distance traveled by both waves is the same, so we can equate the distance for both waves

distance = speed x time

for concrete, distance = 3000 x T for air, distance = 343 x (T + 0.8)

now equating the two distance together we have

3000 x T = 343 x (T + 0.8)

3000T = 343T + 274.4

3000T - 343T = 274.4

T = 0.103 s

recall that distance = 3000 x T = 3000 x 0.103 = 309 m