Quadratic Equations and Factoring

Question

Jorge is kicking a ball straight up into the air. The height of the ball is described by the equation h=-16t^2+20t, where h is the height of the ball and t is the time in seconds. How long will it take the ball to hit the ground?

Answer 1

At the moment the ball hits the ground h = 0

 

therefore -16t² + 20t = 0

 

4t(-4t + 5) = 0

 

either 4t = 0, in which case t = 0

 

or -4t + 5 = 0, in which case t = 5/4 = 1.25 seconds

 

Both answers are correct, h = 0 describes the time t=0 just as the ball is initially kicked into the air.

 

h = 1.25 seconds describes the time taken for the ball to return to earth under the influence of gravity