A soccer player uses her head to hit a ball up in the air from a height of 1 meters with an initial vertical velocity of 5 meters per second. The height h in meters of the ball is given by h = −4.9t2 + 5t + 1, 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? Enter the time to two decimal places.

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Answer:

It will take 1.19 seconds for the ball to hit the ground if no other players touch it

Step-by-step explanation:

The height of the ball after t seconds is given by the following equation:

[tex]h(t) = -4.9t^{2} + 5t + 1[/tex]

How long will it take the ball to hit the ground if no other players touch it?

This is t when h(t) = 0. So

[tex]-4.9t^{2} + 5t + 1 = 0[/tex]

Solving a quadratic equation:

Given a second order polynomial expressed by the following equation:

[tex]ax^{2} + bx + c, a\neq0[/tex].

This polynomial has roots [tex]x_{1}, x_{2}[/tex] such that [tex]ax^{2} + bx + c = a(x - x_{1})*(x - x_{2})[/tex], given by the following formulas:

[tex]x_{1} = \frac{-b + \sqrt{\bigtriangleup}}{2*a}[/tex]

[tex]x_{2} = \frac{-b - \sqrt{\bigtriangleup}}{2*a}[/tex]

[tex]\bigtriangleup = b^{2} - 4ac[/tex]

In this question:

[tex]-4.9t^{2} + 5t + 1 = 0[/tex]

So [tex]a = -4.9, b = 5, c = 1[/tex]

So

[tex]\bigtriangleup = 5^{2} - 4*4.9*1 = 44.6[/tex]

[tex]t_{1} = \frac{-5 + \sqrt{44.6}}{2*(-4.9)} = -0.17[/tex]

[tex]t_{2} = \frac{-5 - \sqrt{44.6}{2*(-4.9)}  = 1.19[/tex]

Since we want a time measure, the answer cannot be negative.

It will take 1.19 seconds for the ball to hit the ground if no other players touch it