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.
+36916 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
