SOLUTION: A rocket is propelled upward from the top of a building 220 feet tall at an initial velocity of 72 feet per second. The function that describes the height of the rocket in terms of

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: A rocket is propelled upward from the top of a building 220 feet tall at an initial velocity of 72 feet per second. The function that describes the height of the rocket in terms of      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


   



Question 732968: A rocket is propelled upward from the top of a building 220 feet tall at an initial velocity of 72 feet per second. The function that describes the height of the rocket in terms of t is f(t)=-16t^2 + 72t +220. Determine both the time at which the rocket reaches its max height and the max height that the rocket reaches.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The curve that the rocket follows is a parabola. The maximum
height is also called the vertex of the parabola. The formula for
the time component of the vertex is +t%5Bv%5D+=+-b%2F%282a%29+, when
the equation looks like +f%28t%29+=+at%5E2+%2B+b%2At+%2B+c+
In this problem,
+a+=+-16+
+b+=+72+
+t%5Bv%5D+=+-72+%2F+%282%2A%28-16%29%29+
+t%5Bv%5D+=+72%2F32+
+t%5Bv%5D+=+2.25+ sec
Now plug this value back into the equation to find +f%282.25%29+
+f%282.25%29+=+-16%2A%282.25%29%5E2+%2B+72%2A2.25+%2B+220+
+f%282.25%29+=+-16%2A5.0625+%2B+162+%2B+220+
+f%282.25%29+=+-81+%2B+162+%2B+220+
+f%282.25%29+=+301+
It reaches a maximum height of 301 ft in 2.25 sec
Here's a plot:
+graph%28+400%2C+400%2C+-1%2C+8%2C+-20%2C+330%2C+-16x%5E2+%2B+72x+%2B+220+%29+