SOLUTION: A ball is thrown vertically upward from the ground. Its distance in feet from the ground in t seconds is s(t)=160t-16t^2. After how many seconds will the ball be 336 feet from theā

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Question 1155669: A ball is thrown vertically upward from the ground. Its distance in feet from the ground in t seconds is s(t)=160t-16t^2. After how many seconds will the ball be 336 feet from theā€‹ ground?
Found 2 solutions by Boreal, ikleyn:
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
s(t)=-16t^2+160t=336
so -16t^2+160t-336=0
or 16t^2-160t+336=0, changing sign and
t^2-10t+21=0 dividing by 16
(t-7)(t-3)=0
at 3 and 7 seconds.
graph%28300%2C300%2C-10%2C10%2C-10%2C400%2C-16x%5E2%2B160x%29

Answer by ikleyn(52898) About Me  (Show Source):
You can put this solution on YOUR website!
.

They want you solve this quadratic equation


    160t - 16t^2 = 336.


Write it in the standard form quadratic equation.


Then solve using the quadratic formula or factoring (if it works) - on your choice.