A ball is thrown vertically upward from the top of a building 160 feet tall with an initial velocity of 48 feet per second. The distance d (in feet) of the ball from the ground after t seconds is d(t) = 160 + 48t – 16t2. a. After how many seconds does the ball strike the ground? Write your answer in a complete sentence with proper grammar and correct spelling. b. When will the ball reach its maximum height?

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Answer

given,

height of the building = 160 ft

initial velocity = 48 ft/s

the relation of distance is given

d = -16 t²  + 48 t + 160

time at which the ball hit the ground will be when d = 0

-16 t²  + 48 t + 160 = 0

solving quadratic equation

[tex]t = \dfrac{-b\pm \sqrt{b^2-4ac}}{2a}[/tex]

[tex]t = \dfrac{-48\pm \sqrt{48^2+4\times 16 \times 160}}{2\times (-16)}[/tex]

[tex]t = \dfrac{-48\pm 112}{-32}[/tex]

[tex]t = \dfrac{-48+ 112}{-32},\dfrac{-48- 112}{-32}[/tex]

t = 5 s(neglecting the negative solution)

b) ball will reach max height when velocity is equal to zero

  [tex]v = \dfrac{dd}{dt}[/tex]

  [tex]v = \dfrac{d}{dt}(-16 t^2+48 t +160)[/tex]

  [tex]v = -32 t + 48[/tex]

    v = 0

     t = 1.5 s

at 1.5 sec the ball will reach at maximum height

A) The number of seconds that it will take for the ball to strike the ground is; t = 5 seconds.

B) The time it will take for the ball to reach its' maximum height is;

t = 1.5 seconds

We are given the distance equation of the ball from the ground after t seconds as; d(t) = 160 + 48t – 16t²

A) The ball will strike the ground at d(t) = 0. Thus;

160 + 48t – 16t² = 0

From online quadratic equation solver, we have the solution to the equation as; t = -2 or t = 5

time cannot be negative and so we will adopt t = 5 s.

Thus, The number of seconds that it will take for the ball to strike the ground is 5 seconds.

B) The maximum height will be reached when the velocity is zero i.e. when the derivative of the distance equation is zero.

Thus;

d'(t) = 48 - 32t

At d'(t) = 0

48 - 32t = 0

32t = 48

t = 48/32

t = 1.5 seconds

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