SOLUTION: Joe drops a rock down a very deep (400 meter) mine shaft in Jarbidge. How long will it take to hear the sound of the rock hitting after he lets go of it? The speed of sound is 343

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Question 1068565: Joe drops a rock down a very deep (400 meter) mine shaft in Jarbidge. How long will it take to hear the sound of the rock hitting after he lets go of it? The speed of sound is 343 meters / second and sound of course is not affected by gravity. You must take the speed of sound into consideration. Answer in seconds. Use the fact that g = 9.8 m/sec^2.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
I will say that +h%280%29+=+400+ m
where +h%28t%29+ is the height in meters
+h%28t%29+=+-%281%2F2%29%2Ag%2At%5E2+%2B+h%280%29+
+h%28t%29+=+-%281%2F2%29%2A9.8%2At%5E2+%2B+400+
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I want to find +t+ when +h%28t%29+=+0+
( the bottom of the well )
+0+=+-4.9t%5E2+%2B+400+
+4.9t%5E2+=+400+
+t%5E2+=+81.6327+
+t+=+9.035+ sec
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After +9.035+ sec, the sound has to travel
+400+ m to Joe's ears
[ time in sec ] = [ distance in meters ] / [ speed in m/sec ]
+400%2F343+=+1.166+ sec
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Add the 2 computed times:
+9.035+%2B+1.166+=+10.2+ sec
Joe hears the sound of the rock
hitting the water in 10.2 sec
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check my math