Question

A soccer player uses her head to hit a ball up in the air from a height of 2 meters with an initial vertical velocity of 5 meters per second. The height h in meters of the ball is given by \large h=-4.9t^2+5t+2 , where t is the time elapsed in seconds. How long will it take the ball to hit the ground if no other players touch it?

Answer 1

Answer:1.32 s

Step-by-step explanation:

Given

The initial height of ball H=2 m

Initial velocity u=5 m/s

Height of ball at any instant is given by

$H=-4.9t^2+5t+2$

The ball will hit the ground when h=0

$-4.9t^2+5t+2=0\\4.9t^2-5t-2=0\\t=\dfrac{5\pm\sqrt{25+4(4.9)(2)}}{2\times 4.9}\\t=\dfrac{5\pm\sqrt{64.2}}{9.8}\\t=\dfrac{5+8.01}{9.8}=1.32\ s\quad\text{Neglecting negative value of t}$