Derek threw a baseball across the field. The path of the ball can be represented by the equation h =-16t ² +75t+5, where t represents the number of seconds the ball was in the air, and h, represents the height of the ball in feet. the baseball was 2 feet above ground after how many seconds?
F 4.5 seconds
G 4.75 seconds
H 4.73 seconds
J 4.8 seconds

Respuesta :

In order to solve this problem, we plug in 2 for h and then solve for t.

[tex]2=-16 t^{2} +75t+5[/tex]

Next, we subtract 2 from both sides.

[tex]-16 t^{2} +75t+3=0[/tex]

Now, we apply the quadratic formula.

[tex]t= \frac{-75+- \sqrt{ 75^{2}-4*-16*3 } }{2*-16} = \frac{-75+- \sqrt{5625+192} }{-32} = \frac{-75+- \sqrt{5817} }{-32} = \frac{-75+-76.27}{-32} [/tex]

Now, we see what T is if we add 76.27 and if we subtract 76.27.  First, let's try adding it.

[tex]t= \frac{-75+76.27}{-32} = \frac{1.27}{-32} =-0.04[/tex]

Obviously, the ball was not in the air for a negative amount of side.  Let's try subtracting 76.27.

[tex]t= \frac{-75-76.27}{-32} = \frac{-151.27}{-32}=4.73 [/tex]

Aha!  We have found our answer.  The ball was in the air for 4.73 seconds, so H is the correct answer.