Waves and sounds, finding the speed of a jet using the speed of sound

  • #1

Homework Statement



A jet is flying horizontally, as the drawing shows. When the plane is directly overhead at B, a person on the ground hears the sound coming from A in the drawing. The average temperature of the air is 20 oC. If the speed of the plane at A is 180 m/s, what is its speed at B, assuming that it has a constant acceleration?

http://edugen.wileyplus.com/edugen/courses/crs2216/art/qb/qu/c16/ch16p_101.gif


Homework Equations


x=1/2(Vo+V)t
V=λ/Period (T)= λ x Frequency
c (speed of sound)= 343 m/s at 20 degrees celsius
T (period)= 2 ∏/ω(angular frequency)

The Attempt at a Solution



first I tried to use the kinematic equation to find the distance between the points A and B but I am stuck because i need the time in order to find the distance (x) between the two points. I think I need to use the pythagorean theorem because the angle made by point B is 90 degrees and I am giving the angle of the observer on the ground as 36 degrees, meaning that the last angle should be 54 degrees to add up to 180 degrees. Do I need to use the law of cosines or sines since I know three angles? any help is appreciated

Homework Statement





Homework Equations





The Attempt at a Solution

 

Attachments

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Answers and Replies

  • #2
Spinnor
Gold Member
2,181
391
Can't view your picture.
 
  • #3
Spinnor
Gold Member
2,181
391
In your image, the right triangle has sides (using your formula), (v_0 + v)*t/2 , h, c*t.

The length (v_0 + v)*t/2 is related to the length c*t using some trig. t will cancel.

This is late, hope it helps.
 

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