Help - Sound question (1 Viewer)

[mathpie]

An observer standing 320 metres from a wall hears a gun fired. Then gun was 80 metres from the wall at the time of firing. After hearing the initial sound, the observer hears the sound reflected form the wall. take the speed of sound in air as 320m/s. What is the time interval between the 2 sounds.

My working:
d1 = 320-80 = 240m (gun straight to observer)
d2 = 320+80 = 400m (gun to wall to observer)

T2-T1 = (d2-d1)/s
= (400-240)/320
= 0.5 s

But the answer is apparently 0.25s?

 

[pikachu975]

An observer standing 320 metres from a wall hears a gun fired. Then gun was 80 metres from the wall at the time of firing. After hearing the initial sound, the observer hears the sound reflected form the wall. take the speed of sound in air as 320m/s. What is the time interval between the 2 sounds.

My working:
d1 = 320-80 = 240m (gun straight to observer)
d2 = 320+80 = 400m (gun to wall to observer)

T2-T1 = (d2-d1)/s
= (400-240)/320
= 0.5 s

But the answer is apparently 0.25s?

Your working out seems right but we'll wait for someone else to verify

 

[Fizzy_Cyst]

An observer standing 320 metres from a wall hears a gun fired. Then gun was 80 metres from the wall at the time of firing. After hearing the initial sound, the observer hears the sound reflected form the wall. take the speed of sound in air as 320m/s. What is the time interval between the 2 sounds.

My working:
d1 = 320-80 = 240m (gun straight to observer)
d2 = 320+80 = 400m (gun to wall to observer)

T2-T1 = (d2-d1)/s
= (400-240)/320
= 0.5 s

But the answer is apparently 0.25s?

Answer is definitely 0.5s!

Reflected sound wave travels an extra 160m as your working shows.

FYI: That question is from the 2000 independent preliminary examination. First question. The answer given was 0.5s, not 0.25s

Whoever gave you that answer has done it incorrectly