Math

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=164t-16t^2. After how many seconds will the rocket first reach a height of 400ft?

asked by Pam
  1. well! , just set
    164t - 16t^2 = 400

    -16t^2 + 164t - 400 = 0
    4t^2 - 41t + 100 = 0
    (t-16)(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)

    posted by Reiny
  2. 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.


    posted by Henry

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