A rocket is launched from the top of a 101-foot cliff with an initial velocity of 116 ft/s. a. Substitute the values into the vertical motion formula h = –16t2 + vt + c. Let h = 0. b. Use the quadratic formula to find out how long the rocket will take to hit the ground after it is launched. Round to the nearest tenth of a second.

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[tex]\bf ~~~~~~\textit{initial velocity} \\\\ \begin{array}{llll} ~~~~~~\textit{in feet} \\\\ h(t) = -16t^2+v_ot+h_o \end{array} \quad \begin{cases} v_o=\stackrel{116}{\textit{initial velocity of the object}}\\\\ h_o=\stackrel{101}{\textit{initial height of the object}}\\\\ h=\stackrel{}{\textit{height of the object at "t" seconds}} \end{cases} \\\\\\ h(t)=-16t^2+116t+101\implies \stackrel{h(t)}{0}=-16t^2+116t+101[/tex]

[tex]\bf ~~~~~~~~~~~~\textit{quadratic formula} \\\\ 0=\stackrel{\stackrel{a}{\downarrow }}{-16}t^2\stackrel{\stackrel{b}{\downarrow }}{+116}x\stackrel{\stackrel{c}{\downarrow }}{+101} \qquad \qquad t= \cfrac{ - b \pm \sqrt { b^2 -4 a c}}{2 a} \\\\\\ t=\cfrac{-116\pm\sqrt{116^2-4(-16)(101)}}{2(-16)} \\\\\\ t=\cfrac{-116\pm\sqrt{116^2-4(-16)(101)}}{2(-16)}\implies t=\cfrac{-116\pm\sqrt{116^2+6464}}{-32} \\\\\\ t\approx \begin{cases} -0.7855696910943375\\ \boxed{8.0355696910943375} \end{cases}[/tex]

It take the rocket 8 seconds to hit the ground after it is launched.

Let h represent the height of the rocket at time t.

The height (h) is given by:

h = –16t² + vt + c

Since the initial velocity (v) = 116 ft/s, the initial height c = 101 ft, hence:

h = –16t² + 116t + 101

Hence, the rocket touches the ground at time h = 0, hence:

0 = -16t² + 116t + 101

Hence, t = 8 seconds.

Therefore it take the rocket 8 seconds to hit the ground after it is launched.

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