document.write( "Question 461883: a ball is thrown from a 180m high cliff> the relation h=-5t^2-5t+180 relates the time in seconds to the height in m. a) What was the intial height of the ball?
\n" ); document.write( "b) how long does it take the ball to reach a height of 80m? c) determine the maximum height if the ball \n" ); document.write( "
Algebra.Com's Answer #316662 by nerdybill(7384)\"\" \"About 
You can put this solution on YOUR website!
a ball is thrown from a 180m high cliff> the relation h=-5t^2-5t+180 relates the time in seconds to the height in m.
\n" ); document.write( "a) What was the intial height of the ball?
\n" ); document.write( "this is when t=0:
\n" ); document.write( "h=-5t^2-5t+180
\n" ); document.write( "h=-5(0)^2-5(0)+180
\n" ); document.write( "h=180 m
\n" ); document.write( ".
\n" ); document.write( "b) how long does it take the ball to reach a height of 80m?
\n" ); document.write( "set h to 80 and solve for t:
\n" ); document.write( "h=-5t^2-5t+180
\n" ); document.write( "80=-5t^2-5t+180
\n" ); document.write( "0=-5t^2-5t+100
\n" ); document.write( "0=-t^2-t+20
\n" ); document.write( "0=t^2+t-20
\n" ); document.write( "0=(t+5)(t-4)
\n" ); document.write( "t={-5,4}
\n" ); document.write( "throw out the negative solution leaving:
\n" ); document.write( "t = 4 seconds
\n" ); document.write( ".
\n" ); document.write( "c) determine the maximum height if the ball
\n" ); document.write( "this occurs at the vertex when
\n" ); document.write( "h=-5t^2-5t+180
\n" ); document.write( "t = -b/(2a)
\n" ); document.write( "t = -(-5)/(2(-5))
\n" ); document.write( "t = 5/(-10)
\n" ); document.write( "t = -1/2 seconds
\n" ); document.write( ".
\n" ); document.write( "Note: you probably typed in a wrong equation in your original problem
\n" ); document.write( "probably should be something like:
\n" ); document.write( "h=-5t^2+5t+180\r
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "
\n" );