Math
posted by Pam
A model rocket is launched with an initial velocity of 164ft/sec. It's height h, in feet, after t seconds is given by the formula h=164t16t^2. After how many seconds will the rocket first reach a height of 400ft?

Reiny
well! , just set
164t  16t^2 = 400
16t^2 + 164t  400 = 0
4t^2  41t + 100 = 0
(t16)(4t  10) = 0
t = 10 or t = 10/4 or 2.5 seconds
So it will reach that height first at 2.5 seconds,
(and again after 10 seconds on its way back down) 
Henry
h = 164t  16t^2 = 400 Ft.
16t^2 + 164t = 400
16t^2 + 164  400 = 0
Use Quadratic Formula and get:
t = 4, and 6.25 seconds.
Answer = 4 s. The rocket is falling when
t = 6.25 s.
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