document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=651539>Question 651539</A>: <I><SPAN STYLE=\"word-break: break-all;\"> the height h(t) of a projectile measured from ground-level is given by<BR>\n" );
document.write( " h(t) = -t^2+8t where t represents the elapsed time in seconds since it was launched \r<BR>\n" );
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document.write( "a) can the projectile hit a target located at a height of 20 cm?<BR>\n" );
document.write( "b) at what instant does the projectile hit the ground?\r<BR>\n" );
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document.write( " </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #407708 by </B><A HREF=/tutors/aboutme.mpl?userid=nerdybill><B>nerdybill(7384)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=nerdybill><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=nerdybill><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=407708\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> the height h(t) of a projectile measured from ground-level is given by<BR>\n" );
document.write( " h(t) = -t^2+8t where t represents the elapsed time in seconds since it was launched \r<BR>\n" );
document.write( "\n" );
document.write( "a) can the projectile hit a target located at a height of 20 cm?<BR>\n" );
document.write( "the max height is at the vertex:<BR>\n" );
document.write( "time at vertex:<BR>\n" );
document.write( "t = -b/(2a)<BR>\n" );
document.write( "t = -8/(2(-1))<BR>\n" );
document.write( "t = -8/(-2)<BR>\n" );
document.write( "t = 4 secs<BR>\n" );
document.write( ".<BR>\n" );
document.write( "height at vertex:<BR>\n" );
document.write( "h(4) = -4^2+8(4)<BR>\n" );
document.write( "h(4) = -16+32<BR>\n" );
document.write( "h(4) = 32 <BR>\n" );
document.write( "since 32 is greater than 20, answer is yes<BR>\n" );
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document.write( "b) at what instant does the projectile hit the ground?<BR>\n" );
document.write( "set h(t) to zero and solve for t:<BR>\n" );
document.write( "h(t) = -t^2+8t<BR>\n" );
document.write( "0 = -t^2+8t<BR>\n" );
document.write( "0 = t(-t+8)<BR>\n" );
document.write( "t = {0, 8}<BR>\n" );
document.write( "answer: 8 seconds\r<BR>\n" );
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