Science Buddies: "Ask an Expert"

A person is standing where the land meets the Atlantic ocean and an airplane flies directly over this person at 500 feet but the person doesn't hear it until 60 seconds has elapsed after it was directly over their head. At what speed would the airplane need to be flying for this to occur? Assume the airplane has unlimited speed potential and the air temperature is 68 degrees.

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Science Buddies

This is not a homework question. I'm a 50 year old retired USAF Veteran who was pondering with a friend while we were discussing the USAF Thunderbirds demonstration team. I was curious as to how to go about figuring out this type of problem from various altitudes and sound delays.

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There are no conditions (reasonable conditions) under which this could happen. First of all, the plane would have to be faster than the speed of sound if you could only hear it after it has passed over you - you can hear sound sources moving towards you, whether it's your dog in the yard, a car on the street, or a passenger plane in the air. Only if the plane is faster than the speed of sound would it be able to outrun the sound and pass over your head before you could hear it.
However, your plane is only 500 ft up - sound will travel this distance in about 0.5 seconds. The plane would have to be about 18 km or 11 miles up in the sky and be supersonic to have a 60 second delay between passing over your head and you hearing the sound for the first time.
So, unless you'd reduce the speed of sound more than 100 -fold with extremely low pressures and extremely low temperature, it's not going to happen

Thank you for that explanation.