Physics help (2 Viewers)

[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?

 

[keepLooking]

[observer]<---------240m-------->[ gun ]<----80m--->[wall]



Edit: I am wrong

 

[mathpie]

for d1, doesn't sound first travel to the wall and then back to the observer? so 80+80+240 = 400

 

[pikachu975]

for d1, doesn't sound first travel to the wall and then back to the observer? so 80+80+240 = 400

Yeah your answer of 0.5 is right.

 

[keepLooking]

for d1, doesn't sound first travel to the wall and then back to the observer? so 80+80+240 = 400

You are definitely correct.