Question 143954
s(t) = -16t^2+ vot
Comment: s(t) is the height of the projectile after t seconds.
vo=96 ft/sec is the velocity of the projectile when you let go of it. 
::: IN NUMBER 25, FIND THE TIME (t) THAT THE PROJECTILE WILL 
(a)REACH A HEIGHT OF 80ft :
80 = -16t^2 + 96t
-16t^2+96t-80= 0
-16(t^2-6t+5)=0
(t-1)(t-5)=0
t = 1 or t=5
The projectile reaches a height of 80 ft. after 1 second (on the way up)
and at 5 seconds (on the way down).
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(b) RETURN TO THE GROUND FOR THE GIVEN VALUE OF v0=96 ft/sec. 
ROUND ANSWERS TO THE NEAREST HUNDREDTH IF NECESSARY.
-16t^2+96t=0
-16t(t-6)=0
t = 0 or t=6
It's on the ground at time=0 and again at time = 6 seconds.
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Cheers,
Stan H.
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Cheers,
Stan H.