The equation y = -16t^2 + 28t + 144 describes the height (in feet) of a ball tossed up in the air at 28 feet per second from a height of 144 feet from the ground. In how many seconds will the ball hit the ground?
When it hits the ground, y = 0....so....
-16t^2 + 28t + 144 = 0 divide through by -4
4t^2 - 7t - 36 = 0 factor
(4t + 9) ( t - 4) = 0
Only the second factor will produce a positive value for t
t - 4 = 0
t = 4 sec