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Doppler Effect Physics Waves Physics Class 11th

A driver in a car, approaching a vertical wall notices that the frequency of his car horn, has changed from 400 Hz $\frac{}{_{}} \frac{}{_{}^{}}$ to 400 Hz $\frac{}{_{}^{}}$ , when it gets reflected from the wall. If the speed of sound in air is 345 m/s , then the speed of the car is:

Option 1 -

24 km/hr

Option 2 -

36 km/hr

Option 3 -

18 km/hr

Option 4 -

54 km/hr

3 Views | Posted 2 months ago

Asked by Shiksha User

1 Answer

Answered by

Vishal Baghel | Contributor-Level 10

2 months ago

Correct Option - 4

Detailed Solution:

f? = frequency heard by wall = f_s (v_s/ (v_s - v_c)
f? = frequency heard by driver after reflection from wall

f? = (v_s + v_c)/v_s)f? = (v_s + v_c)/ (v_s - v_c)f?
f? /f? = (v_s - v_c)/ (v_s + v_c)
48/44 = (v_s - v_c)/ (v_s + v_c)
12 (v_s + v_c) = 11 (v_s - v_c)
23v_c = v_s
v_c = v_s/23 = 345/23 = 15 m/s
= (15 × 18)/5 = 54 km/hr

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A driver in a car, approaching a vertical wall notices that the frequency of his car horn, has changed from 400 Hz $\frac{}{_{}} \frac{}{_{}^{}}$ to 400 Hz $\frac{}{_{}^{}}$ , when it gets reflected from the wall. If the speed of sound in air is 345 m/s , then the speed of the car is:

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A driver in a car, approaching a vertical wall notices that the frequency of his car horn, has changed from 400 Hz to 400 Hz , when it gets reflected from the wall. If the speed of sound in air is 345 m/s , then the speed of the car is:

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A driver in a car, approaching a vertical wall notices that the frequency of his car horn, has changed from 400 Hz $\frac{}{_{}} \frac{}{_{}^{}}$ to 400 Hz $\frac{}{_{}^{}}$ , when it gets reflected from the wall. If the speed of sound in air is 345 m/s , then the speed of the car is: