Answer:
[tex]Time = 7.5\ seconds[/tex]
Step-by-step explanation:
Given
[tex]Equation:\ h(t) = -16t^2 + 120t[/tex]
[tex]Initial\ Velocity = 160ft/s[/tex]
Required:
Determine the time taken to return to the ground
From the equation given; height (h) is a function of time (t)
When the rocket returns to the ground level, h(t) = 0
Substitute 0 for h(t) in the given equation
[tex]h(t) = -16t^2 + 120t[/tex]
becomes
[tex]0 = -16t^2 + 120t[/tex]
Solve for t in the above equation
[tex]-16t^2 + 120t = 0[/tex]
Factorize the above expression
[tex]-4t(4t - 30) = 0[/tex]
Split the expression to 2
[tex]-4t = 0\ or\ 4t - 30 = 0[/tex]
Solving the first expression
[tex]-4t = 0[/tex]
Divide both sides by -4
[tex]\frac{-4t}{-4} = \frac{0}{-4}[/tex]
[tex]t = \frac{0}{-4}[/tex]
[tex]t =0[/tex]
Solving the second expression
[tex]4t - 30 = 0[/tex]
Add 30 to both sides
[tex]4t - 30+30 = 0+30[/tex]
[tex]4t = 30[/tex]
Divide both sides by 4
[tex]\frac{4t}{4} = \frac{30}{4}[/tex]
[tex]t = \frac{30}{4}[/tex]
[tex]t = 7.5[/tex]
Hence, the values of t are:
[tex]t =0[/tex] and [tex]t = 7.5[/tex]
[tex]t =0[/tex] shows the time before the launching the rocket
while
[tex]t = 7.5[/tex] shows the time after the rocket returns to the floor
