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Question

If an object is shot upward from the ground with an initial velocity of v₀

 feet per second, then its height after t seconds (until it hits the ground) is given by

H = v_ot − 16t² feet.

A firework device is fired upward at a rate of 90 feet per second. You can see the device from your apartment window when it is 40 feet or higher. During what time span can you view the device?

Answer 1

40 = 90t - 16t^2

16t^2 -90t +40 = 0

8t^2 - 45t +20 = 0

t = 45/16 + or - (1/16)sqr(45^2 -4(8)(20))

= 5.14 or 0.49 seconds

for 4.65 seconds the object is viewable at 40 feet high or more