Sound Waves conical wavefront questions help!

https://isaacphysics.org/questions/conical_wavefront?board=78ba0383-72e8-403e-8a83-e5a3092c174c&stage=a_level
I got te first part, but I am confused about how to calculate the time delay
Cause I calculated the time it takes the sound from when it's overhead to reach the person (14.7 s) but they said that it was wrong
Could you explain what they mean by time delay?
Thank you so much!

Reply 1

Joinedup

The first aircraft sound you hear when the fast moving aircraft is overhead is from the sound waves that left the aircraft before it was overhead.

Reply 2

MayaVellichor

Original post by Joinedup

The first aircraft sound you hear when the fast moving aircraft is overhead is from the sound waves that left the aircraft before it was overhead.

Ah OK so am I drawing a right angle triangle with the vertical height, vt of plane, ct of sound
But then the ct of sound would be on the hypotenuse but it can't be cause the plane is moving faster therefore covering a greater distance

Reply 3

Joinedup

I'll adapt a diagram that I stole from here https://www.grc.nasa.gov/www/k-12/airplane/machang.html

I'm trying to show the point in time when the plane (arrowhead) is directly overhead of the observer, X is the point on the wavefront behind and below the plane that's heading towards the observer.