Discover answers to your most pressing questions at Westonci.ca, the ultimate Q&A platform that connects you with expert solutions. Get expert answers to your questions quickly and accurately from our dedicated community of professionals. Get detailed and accurate answers to your questions from a dedicated community of experts on our Q&A platform.

An object is thrown upward at a speed of 136 feet per second by a machine from a height of 18 feet off the ground. The height [tex]h[/tex] of the object after [tex]t[/tex] seconds can be found using the equation [tex]h = -16t^2 + 136t + 18[/tex].

1. When will the height be 252 feet?
[tex]\square[/tex] Select an answer

2. When will the object reach the ground?
[tex]\square[/tex] Select an answer

Sagot :

To solve these problems, we will use the equation for height, [tex]\( h = -16t^2 + 136t + 18 \)[/tex], where [tex]\( t \)[/tex] is the time in seconds.

### Part 1: When will the height be 252 feet?
We need to determine the value(s) of [tex]\( t \)[/tex] when [tex]\( h = 252 \)[/tex]:
[tex]\[ 252 = -16t^2 + 136t + 18 \][/tex]

Rearranging this equation, we get:
[tex]\[ -16t^2 + 136t + 18 - 252 = 0 \][/tex]
[tex]\[ -16t^2 + 136t - 234 = 0 \][/tex]

This is a quadratic equation of the form [tex]\( at^2 + bt + c = 0 \)[/tex], where:
[tex]\[ a = -16 \][/tex]
[tex]\[ b = 136 \][/tex]
[tex]\[ c = -234 \][/tex]

We solve this using the quadratic formula:
[tex]\[ t = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \][/tex]

Substituting for [tex]\( a \)[/tex], [tex]\( b \)[/tex], and [tex]\( c \)[/tex]:
[tex]\[ t = \frac{-136 \pm \sqrt{136^2 - 4(-16)(-234)}}{2(-16)} \][/tex]

Solving the discriminant part [tex]\( b^2 - 4ac \)[/tex] first:
[tex]\[ 136^2 = 18496 \][/tex]
[tex]\[ -4 \cdot (-16) \cdot (-234) = 14976 \][/tex]
[tex]\[ b^2 - 4ac = 18496 - 14976 = 3520 \][/tex]

Thus, the equation for [tex]\( t \)[/tex] becomes:
[tex]\[ t = \frac{-136 \pm \sqrt{3520}}{-32} \][/tex]

Simplifying:
[tex]\[ \sqrt{3520} = \sqrt{16 \cdot 220} = 4\sqrt{220} \][/tex]

So,
[tex]\[ t = \frac{-136 \pm 4\sqrt{220}}{-32} \][/tex]
[tex]\[ t = \frac{-136 + 4\sqrt{220}}{-32}, \quad t = \frac{-136 - 4\sqrt{220}}{-32} \][/tex]

Further simplifying:
[tex]\[ t = \frac{-136 + \sqrt{3520}}{-32} = \frac{-136}{-32} + \frac{4\sqrt{220}}{-32} \][/tex]
[tex]\[ t = \frac{136}{32} - \frac{\sqrt{220}}{8} \][/tex]
[tex]\[ t = \frac{255}{32} - \frac{\sqrt{220}}{8} \][/tex]

The solutions [tex]\( t \)[/tex] are:
[tex]\[ t = \frac{17}{4} - \frac{\sqrt{55}}{4}, \quad t = \frac{17}{4} + \frac{\sqrt{55}}{4} \][/tex]

Therefore, the height will be 252 feet at:
[tex]\[ t = \frac{17}{4} - \frac{\sqrt{55}}{4} \][/tex]
[tex]\[ t = \frac{17}{4} + \frac{\sqrt{55}}{4} \][/tex]

### Part 2: When will the object reach the ground?
We need to determine the value(s) of [tex]\( t \)[/tex] when [tex]\( h = 0 \)[/tex]:
[tex]\[ 0 = -16t^2 + 136t + 18 \][/tex]

Solving the quadratic equation:
[tex]\[ -16t^2 + 136t + 18 = 0 \][/tex]

Using the same quadratic formula:
[tex]\[ t = \frac{-136 \pm \sqrt{136^2 - 4(-16)(18)}}{2(-16)} \][/tex]

Solving the discriminant:
[tex]\[ 136^2 = 18496 \][/tex]
[tex]\[ -4 \cdot (-16) \cdot 18 = 1152 \][/tex]
[tex]\[ b^2 - 4ac = 18496 + 1152 = 19648 \][/tex]

Thus:
[tex]\[ t = \frac{-136 \pm \sqrt{19648}}{-32} \][/tex]

Simplifying:
[tex]\[ \sqrt{19648} = \sqrt{64 \cdot 307} = 8\sqrt{307} \][/tex]

So,
[tex]\[ t = \frac{-136 \pm 8\sqrt{307}}{-32} \][/tex]
[tex]\[ t = \frac{-136}{-32} + \frac{8\sqrt{307}}{-32} \][/tex]
[tex]\[ t = \frac{17}{4} - \frac{\sqrt{307}}{4} \][/tex]

The solutions [tex]\( t \)[/tex] are:
[tex]\[ t = \frac{17}{4} - \frac{\sqrt{307}}{4}, \quad t = \frac{17}{4} + \frac{\sqrt{307}}{4} \][/tex]

Therefore, the object will reach the ground at:
[tex]\[ t = \frac{17}{4} - \frac{\sqrt{307}}{4} \][/tex]
[tex]\[ t = \frac{17}{4} + \frac{\sqrt{307}}{4} \][/tex]

These results give us the times at which the height is 252 feet and when the object reaches the ground.