Question 713947: A projectile is launched straight up from the ground level with an initial velocity of 96 ft per second. Its height in feet, "s", after "t" seconds is given by the equation: s=16t^2+96t
a) At what time(s) will it reach a height of 80 feet?
b) After how many seconds will it return to the ground?
I haven't shown any work because it is a challenge problem that they are having us get "help" with to prepare for a later chapter, to get us thinking. I have been searching through the book and can't find a word problem that deals with velocity. Please help or at least help me understand how to even begin to solve it. Thank you!
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! A projectile is launched straight up from the ground level with an initial velocity of 96 ft per second. Its height in feet, "s", after "t" seconds is given by the equation: s=16t^2+96t
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It's -16t^2 + 96t
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a) At what time(s) will it reach a height of 80 feet?
-16t^2 + 96t = 80
Solve for t
-16t^2 + 96t = 80
t^2 - 6t + 5 = 0
(t-5)*(t-1) = 0
t = 1 second (going up)
t = 5 seconts (coming back down)
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b) After how many seconds will it return to the ground?
Same equation, equals 0
solve for t
t = 0 is the time at launch
The 2nd value of t is at impact.
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