The Doppler effect is the right concept to solve this problem. The Doppler effect is understood as the change in apparent frequency of a wave produced by the relative movement of the source with respect to its observer. Mathematically it can be described as,
![f = (1-\frac{v_0}{v})f_0](https://tex.z-dn.net/?f=f%20%3D%20%281-%5Cfrac%7Bv_0%7D%7Bv%7D%29f_0)
Here,
= Frequency of the sound from the Whistle
f = Frequency of sound heard
v = Speed of the sound in the Air
Replacing we have that
![1- \frac{v_0}{343} = \frac{20kHz}{21kHz}](https://tex.z-dn.net/?f=1-%20%5Cfrac%7Bv_0%7D%7B343%7D%20%3D%20%5Cfrac%7B20kHz%7D%7B21kHz%7D)
![\frac{v_0}{343} = 1-\frac{20}{21}](https://tex.z-dn.net/?f=%5Cfrac%7Bv_0%7D%7B343%7D%20%3D%201-%5Cfrac%7B20%7D%7B21%7D)
![\frac{v_0}{343} = \frac{1}{21}](https://tex.z-dn.net/?f=%5Cfrac%7Bv_0%7D%7B343%7D%20%3D%20%5Cfrac%7B1%7D%7B21%7D)
![v_0 = \frac{1}{21}(343)](https://tex.z-dn.net/?f=v_0%20%3D%20%5Cfrac%7B1%7D%7B21%7D%28343%29)
![v_0 = 16.33m/s](https://tex.z-dn.net/?f=v_0%20%3D%2016.33m%2Fs)
Therefore the minimum speed to know if the whistle is working is 16.33m/s
Answer:
the answers is 67 millimeter plz put me brain list
Answer:
the answer is lucid dreamers ..hope it helped you dear
The Lens Changes Shape to Focus Near Objects. Light rays from objects that are close to the eye are not parallel. Therefore, the eye must bend them more in order to focus the rays on the retina. To accomplish this, the lens change shape.
<h3>Hope this helps</h3>