document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1068891>Question 1068891</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Peter drops a stick of dynamite down a deep hole near Spruce Mountain.  He times it from the moment he lets go and hears the sound exactly 11.20 seconds later.  If the speed of sound is 343 meters / second, how deep is this hole?  You must take the speed of sound into consideration. Answer in meters.  Use g = 9.8 m/sec^2.  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #684158 by </B><A HREF=/tutors/aboutme.mpl?userid=ankor@dixie-net.com><B>ankor@dixie-net.com(22740)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ankor@dixie-net.com><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=ankor@dixie-net.com><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=684158\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Peter drops a stick of dynamite down a deep hole near Spruce Mountain.<BR>\n" );
document.write( " He times it from the moment he lets go and hears the sound exactly 11.20 seconds later.<BR>\n" );
document.write( " If the speed of sound is 343 meters / second, how deep is this hole?<BR>\n" );
document.write( " You must take the speed of sound into consideration.<BR>\n" );
document.write( " Answer in meters. Use g = 9.8 m/sec^2. <BR>\n" );
document.write( ":<BR>\n" );
document.write( "The stick and the sound travel the same distance; dist = speed * time<BR>\n" );
document.write( "let t = stick drop time<BR>\n" );
document.write( "then<BR>\n" );
document.write( "(11.2-t) = sound travel time<BR>\n" );
document.write( ":<BR>\n" );
document.write( "4.9t^2 = 343(11.2-t)<BR>\n" );
document.write( "4.9t^2 = 3841.6 - 343t<BR>\n" );
document.write( "a quadratic equation<BR>\n" );
document.write( "4.9t^2 + 343t - 3841.6<BR>\n" );
document.write( "Using the quadratic formula, I got a positive solution of<BR>\n" );
document.write( "9.82 seconds for the stick to drop<BR>\n" );
document.write( "then<BR>\n" );
document.write( "11.2 - 9.82 = 1.38 seconds for sound to travel back to the surface<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Find the depth of the hole<BR>\n" );
document.write( "343 * 1.38 = 473 meters deep <BR>\n" );
document.write( ":<BR>\n" );
document.write( "Check this by using the falling time of the stick<BR>\n" );
document.write( "4.9(9.82^2) = 473 meter also<BR>\n" );
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document.write( "A student pointed out that my first solution is not correct.<BR>\n" );
document.write( " On thinking it over, I should have used 4.9t^2 for a dropped object, not 9.8 as given.<BR>\n" );
document.write( ":<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );