# physics

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If you drop a stone into a well that is d = 128.0 m deep, how soon after you drop the stone will you hear it hit the bottom of the well?

• physics -

g = acceleration = -9.8 m^s^2
z = height = zo - Vo t - (1/2)(9.8)t^2
z = final height = -128
zo = initial height = 0
Vo = starting velocity = 0
so
-128 = -4.9 t^2
t^2 = 128/4.9
t = 5.11 seconds

• physics -

Since the sound still needs to travel back up the well, it will actually take longer than 5.11 seconds.

v=d/t

343=128/t

t=0.37

5.11+0.37=5.48 seconds.

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