document.write( "Question 1144427: A model rocket is launched upward with an initial velocity of 240 feet per second. The height, in feet, of the rocket t seconds after the launch is given by
\n" ); document.write( "h = −16t2 + 240t.
\n" ); document.write( " How many seconds after the launch will the rocket be 300 feet above the ground? Round to the nearest tenth of a second. \n" ); document.write( "

Algebra.Com's Answer #765538 by ikleyn(52781) $\"\"$ $\"About$

You can put this solution on YOUR website!
.
\n" ); document.write( "

\r\n" );
document.write( "To solve the problem, you need to solve the equation\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "    h = 300,\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "which is\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "    -16t^2 + 240t = 300,    or\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "    16t^2 -240t + 300 = 0\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "     4t^2 - 60t + 75 = 0.\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "Solve it using quadratic formula.\r\n" );
document.write( "\r\n" );
document.write( "The discriminant   b^2 - 4ac = (-60)^2 - 4*4*75 = 2400 is positive, so you will have two different solutions.\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "One of them is the time when the body moves up; the other is the time when the body falls down.\r\n" );
document.write( "

\r
\n" ); document.write( "\n" ); document.write( "Happy calculations (!)\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "

\n" );