Question 889062: A projectile is launched from the ground with an initial velocity of V0 feet per second. Neglecting air resistance, its height in feet per seconds after launch is given by s = -16t^2 +V0t. Find the time(s) that the projectile will
(a) reach a height of 240ft and
(b) return to the ground when V0= 128 feet per second.
Answer by lwsshak3(11628)   (Show Source):
You can put this solution on YOUR website! A projectile is launched from the ground with an initial velocity of V0 feet per second. Neglecting air resistance, its height in feet per seconds after launch is given by s = -16t^2 +V0t. Find the time(s) that the projectile will
(a) reach a height of 240ft and
(b) return to the ground when V0= 128 feet per second.
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set height,s=240
(a) 240=-16t^2+128t
-16t^2+128t-240=0
-t^2+8t-15=0
t^2-8t+15=0
(t-5)(t-3)=0
t=5
or
t=3
projectile will reach a height of 240ft after 3 sec on the way up and after 5 sec on the way down
..
set height,s=0
(b) -16t^2+128t=0
-t^2+8t=0
-t(t-8)=0
t=0 (reject)
or
t=8
projectile will return to the ground after 8 sec
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