# Physics

A supersonic jet travels at 3.0 Mach (i.e. at three times the speed of sound). It cruises at 20,000 m above the ground. we choose t=0 when the plane passes directly overhead of an observer. At what time t will the observer hear the plane?

-- there is a diagram of a person standing on the ground, a plane above him and the distance from him to the plane(vertial) is h (20,000 m). there is a line from the tail of the plane( x axis direction) and and a line from the plane to the ground, at an angle theta to the x axis..

.. i am extremely confused with this question, any guidance would be helpful.

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1. The sound reaches you at the speed of sound after the plane passes overhead. You will not hear the plane until it has gone much further since it is going faster than a sound wave but it still takes the sound 20,000 meters/speed of sound to reach you from overhead.
The triangle shows where behind the plane the plane can be heard.
You will hear a loud bang because all the sound that would normally be radiated in front of the plane is concentrated along that line. It can not get ahead of the line because the line is moving faster than sound.

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