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A boy drops a 0.10 kg stone down a 150 m well and listens for the echo. The air temperature is 20°C. How long after the stone is dropped will the boy hear the echo? The speed of sound through air at 20°C is v = 343 m/s.

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 Mar 14, 2020
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The stone has to travel down 150 m to strike

 

x = 1/2 at^2  

150 = 1/2 (9.81)t^2      t = 5.53 sec

 

Then the sound waves have to travel 150 m

 

150 m / 343 m/s = .437 s

 

5.53 + .437 = 5.96  sec

 Mar 14, 2020

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