SOLUTION: The formula for the height (in feet from the starting point) reached after t seconds by an object thrown upward at r feet per second is h=rt – 16t^2. So for an object thrown upward

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Question 765101: The formula for the height (in feet from the starting point) reached after t seconds by an object thrown upward at r feet per second is h=rt – 16t^2. So for an object thrown upward at 160ft/sec, h=160t-16t^2
after how many seconds will the object first be 336ft above its starting point?
how high will the object be after 4 seconds?
Answer by nerdybill(7384) About Me  (Show Source):
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The formula for the height (in feet from the starting point) reached after t seconds by an object thrown upward at r feet per second is h=rt – 16t^2. So for an object thrown upward at 160ft/sec, h=160t-16t^2
after how many seconds will the object first be 336ft above its starting point?
start with:
h=160t-16t^2
set h to 336 and solve for t:
336=160t-16t^2
dividing both sides by 16:
21 = 10t-t^2
t^2+21 = 10t
t^2-10t+21 = 0
(t-3)(t-7) = 0
t = {3, 7}
the object will be at 336 feet twice (once on the way up and again on the way down) at:
3 seconds and 7 seconds
.
how high will the object be after 4 seconds?
start with:
h=160t-16t^2
set t to 4 and solve for h:
h=160(4)-16(4)^2
h=640-16(16)
h=640-256
h= 384 feet