If I drop a vibrating 440 Hz tuning fork down the elevator shaft

[david90]

if I drop a vibrating 440 Hz tuning fork down the elevator shaft of a tall building and when I hear a freq. of 400 Hz, is it possible to determine how far has the tuning fork fallen? My friend said yes but I think no. Am i right?

 

[chroot]

Yep. You can use the frequency to find the velocity (via the Doppler effect) and the velocity to find the time in gravitational free fall and thus the distance. (Neglecting air resistance and so on in normal physical fashion.)

- Warren

 

[david90]

u have proof of that?

 

[chroot]

Proof? I'm afraid the scientific definition of the word 'proof' doesn't apply here.

- Warren

 

[damgo]

The Doppler shift here is given by freq0*vs / (vs+vfork) where vs~345 m/s, the speed of sound. so 400/440 = 345/(345+vfork).

Then you use distance=vfork^2/19.6

 

[Alexander]

Actually due to time delay for sound to get to you it is not h(v)=(v²/2g) but h(v)=(v²/2g)(1+v/2c)²