Amy, standing near a straight road, records the sound of the horn of a car trave

Question

Amy, standing near a straight road, records the sound of the horn of a car traveling at a constant speed. The recorded frequency as a function of the car's position along the road for trials at different car speeds is accurately graphed below.

Part A:

1.The speed in trial Q is ..... that in U.
2.When the car is far away, the average of the frequencies moving in and out is ..... the frequency at rest.
3.The speed in trial Q is ..... to that in R.
4.The speed in trial S is ..... that in other trials.
5.The distance of Amy from the path in Q is ..... in R.
6.The speed in trial T is ..... that in other trials.

(answer with
Greater than /Less than /Equal to )

Part B

Using the data on the figure, calculate the speed of the car in trial U. Use 340 m/s for the speed of sound.

please show your steps.

please make sure your answer is correct.

Explanation / Answer

Part A:

All of it is governed by simple principle. The faster the car, the further the change in frequency of horn as listened by Amy. So the further the graph saturates from 900 Hz, the faster is the car. As long as car is far away. The distance of Amy from the path doesn't effect the change in frequency, only car's speed effects the change in frequency. So while comparing speeds of cars check for saturating value of frequency in the graph when car is far away from Amy.

1) Less than

2) Greater than since v^2/(v^2 - vsource^2) is greater than 1. So average value would be this factor times the original frequency which would be greater than original frequency.

3) Equal to

4) Less than

5) Less than. She is closer to Q's path since frequency changed much faster as car approached her. You can see a sharp slope in the graph when car approached near Amy.

6) Greater than

P.s. Feel free to ask reasons. I guess you posted this to cross check your answer. If you want clarification on anything please ask. Check http://hyperphysics.phy-astr.gsu.edu/hbase/sound/dopp.html for further reading into doppler effect

Part B:

v=340 m/s is velocity of sound. In trial U observed frequency of horn when car is approaching is 1020 Hz. And at meeting point it would be the actual frequency of horn is 900 Hz.

Using fobserved = f * (v/(v-vsource)) for approaching source

1020 = 900 * (340/ (340 - vsource))

vsource = 40 m/s

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