14) A rocket leaves a launcher at a height of 7 feet off the ground with an initial velocity of 144 feet
per second. The equation describing the rocket's height after t seconds is h = -16t^2+ 144t + 7.
a) Find the maximum height reached by the rocket.
b) How many seconds does it take for the rocket to reach that height?

Respuesta :

a) The maximum height reached by the rocket = 331 ft

b) Time taken for the rocket to reach maximum height = 4.5 seconds

The maximum height is when the speed is 0m/s

That is, dh/dt = 0

[tex]h = -16t^2+144t+7[/tex]

Find dh/dt

[tex]\frac{dh}{dt} = -32t+144[/tex]

At maximum height, dh/dt = 0

0  =  -32t  +  144

32t   =  144

t    =  144/32

t   =   4.5

The rocket reaches the maximum height after 4.5 seconds

Substitute t = 4.5 into h = -16t² + 144t + 7 to find the maximum height

h = -16(4.5²)  + 144(4.5) + 7

h  =  -324   +  648 + 7

h  =  331 feet

The maximum height reached by the rocket = 331 ft

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