document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=83818>Question 83818</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A ball is thrown upward from the roof of a building 100 m tall with an initial velocity of 20 m/s.  When will the ball reach a height of 80 m? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #60313 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=60313\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A ball is thrown upward from the roof of a building 100 m tall with an initial velocity of 20 m/s. When will the ball reach a height of 80 m?<BR>\n" );
document.write( ":<BR>\n" );
document.write( "The equation for this: h(x) height and x = time in seconds <BR>\n" );
document.write( "h(x) = -4.9x^2 + 20x + 100<BR>\n" );
document.write( ":<BR>\n" );
document.write( "To find time when ball is 80 m above the ground:<BR>\n" );
document.write( "-4.9x^2 + 20x + 100 = 80<BR>\n" );
document.write( ":<BR>\n" );
document.write( "-4.9x^2 + 20x + 100 - 80 = 0<BR>\n" );
document.write( ":<BR>\n" );
document.write( "-4.9x^2 + 20x + 20 = 0<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Solve for x to find the time (in seconds) it will be 80 ft above the ground<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Use the quadratic formula; a=-4.9, b=20, c=20<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%28-20+%2B-+sqrt%28+20%5E2+-+4+%2A+-4.9+%2A+20+%29%29%2F%282%2A-4.9%29+ ALIGN=MIDDLE  ALT=\"x+=+%28-20+%2B-+sqrt%28+20%5E2+-+4+%2A+-4.9+%2A+20+%29%29%2F%282%2A-4.9%29+\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( ":<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%28-20+%2B-+sqrt%28+400+-+%28-392%29%29%29%2F%28-9.8%29+ ALIGN=MIDDLE  ALT=\"x+=+%28-20+%2B-+sqrt%28+400+-+%28-392%29%29%29%2F%28-9.8%29+\"   DISABLED_style= \"max-width:90%; height:auto;\" >; minus a minus = +<BR>\n" );
document.write( ":<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%28-20+-+sqrt%28+792%29%29%2F%28-9.8%29+ ALIGN=MIDDLE  ALT=\"x+=+%28-20+-+sqrt%28+792%29%29%2F%28-9.8%29+\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( ":<BR>\n" );
document.write( "Do the math here you should get a positive solution of;<BR>\n" );
document.write( ":<BR>\n" );
document.write( "x = 4.9 seconds for it to be at 80 m <BR>\n" );
document.write( ":<BR>\n" );
document.write( "A graphical presentation of this event:<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=+graph%28+300%2C+200%2C+-2%2C+8%2C+-10%2C+125%2C+-4.9x%5E2+%2B+20x+%2B+100%29+ ALIGN=MIDDLE  ALT=\"+graph%28+300%2C+200%2C+-2%2C+8%2C+-10%2C+125%2C+-4.9x%5E2+%2B+20x+%2B+100%29+\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( ":<BR>\n" );
document.write( "Notice that when x = 5 sec, it will be at about 80 meters (y)<BR>\n" );
document.write( "Also notice that it will be 20 meters below the height of the building (x=0)<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Did this make sense to you? </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );