# physics

To estimate how high the cliff is you throw a rock off the edge and 7.8 s later you hear the rock hit the ground. The speed of sound is 330 m/s. Ignoring air resistance how high is the cliff?

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1. h = (1/2)(9.81)(tfall)^2
h = 330 (7.8-tfall)

660 (7.8-tfall) = 9.81 tfall^2

9.81 tf^2 + 660 tf - 5148 = 0

for the positive root I get 7.06
so the sound comes up for
7.8 - 7.06 = .7407 seconds
.7404*330 = 244 meters

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posted by Damon

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