Question

A whistle you use to call your hunting dog has a frequency of 21 khz, but your dog is ignoring it. you suspect the whistle may not be working, but you can't hear sounds above 20 khz. to test it, you ask a friend to blow the whistle, then you hop on your bicycle.
At what minimum speed should you ride to know if the whistle is working?

Answer 1

Answer:

Explanation:

Given

Frequency of whistle $f_0=21\ kHz$

Human hearing frequency $f=20\ kHz$

When a source or observer moves relative to each other then there is change in apparent frequency which is given by

$f'=f_0\frac{v-v_0}{v+v_s}$

where v=velocity of sound(340 m/s )

$v_0$=velocity of observer

$v_s$=velocity of source

$f'$=apparent frequency

$f_0$=original Frequency

$20=21\times \frac{340-v_0}{340}$

$323.809=340-v$

$v=16.19\ m/s\approx 16.2\ m/s$