mj1423 2 years ago A student, standing near a straight road, records the sound of a car’s horn. The recorded frequency (as a function of the car’s position along the road) is plotted in the fig- ure below. The same car made four trial runs along the road. Each trial was made with the car traveling at a constant speed. The four re- sults are plotted below, denoted by the curves G, D, Q, and N.

1. mj1423

2. mj1423

Lowest Speed? Speed in Trial D compared to G? Speed in Trial Q compared to D? Which trial did the student stand closest to the road?

3. Mashy

This requires an understanding of doppler effect.. when a car is speeding towards you.. the frequency of the sound as heard by you goes up.. now.. if the speed is higher, then the observed frequency is also higher.. and when the car goes past you.. the frequency goes down... similarly here also.. if the speed is higher, the frequency would be lower.. can you solve it now?

4. Mashy

|dw:1359796494853:dw|

5. mj1423

Lowest Speed? N Speed in Trial D compared to G? Less than G Speed in Trial Q compared to D? is less than D Which trial did the student stand closest to the road? N Is that Correct? And I'm gonna post a figure for my problem

6. mj1423

7. mj1423

and on the closest to the road question. I'm gonna change my answer to unable to be determine

8. Mashy

if you are very close to the road.. then shift would be faster.. hence you would get a SHARP change in the frequency .. if you were farter away.. the shift would be more gradual.. hence your graph would show you a gradual change.. . so which shows you a SHARP change.. and you got Q and D wrong.. the first answer is right and second answer is also right.. 3rd one wrong.. and 4th one now try to answer

9. Mashy

|dw:1359829846042:dw| hope you notice what m trying to show in the drawing..

10. mj1423

Yes that drawing helps! on the closest to the road it would be G Speed in Trial Q compared to D? The same as D (I'm not sure about that one)

11. Mashy

Q and D are same.. as you said.. but the closest is wrong :P.. sharp change is given by D right?.. see its alomst.. straight horizontal line , then vertical and then again straight.. thats a very sharp change :)

12. mj1423

Yeah i noticed that after i answered the the relationship between Q and D. I forgot to go back and change it lol. I have one more question If you took the average frequency of the before and after it passes the student. Wouldn't it equal the frequency of the horn at rest?