SOLUTION: A ball is thrown in the air from the top of a building. Its height, in meters above ground, as a function of time, in seconds, is given by h(t) = −4.9t2 + 16t + 14. How long

Algebra ->  Logarithm Solvers, Trainers and Word Problems -> SOLUTION: A ball is thrown in the air from the top of a building. Its height, in meters above ground, as a function of time, in seconds, is given by h(t) = −4.9t2 + 16t + 14. How long       Log On


   



Question 1154460: A ball is thrown in the air from the top of a building. Its height, in meters above ground, as a function of time, in seconds, is given by
h(t) = −4.9t2 + 16t + 14.
How long does it take to reach maximum height? (Round your answer to three decimal places.)

Found 2 solutions by josmiceli, ikleyn:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+h%28t%29+=+-4.9t%5E2+%2B+16t+%2B+14+
When the equation has the form:
+y+=+a%2Ax%5E2+%2B+b%2Ax+%2B+c+, then
the formula for the t -value of the vertex
( max or min )
is:
+t%5Bmax%5D+=+-b%2F%282a%29+
+a+=+-4.9+
+b+=+16+
+t%5Bmax%5D+=+-16+%2F+%28+2%2A%28-4.9+%29%29+
+t%5Bmax%5D+=+1.63265+ sec
It takes 1.633 sec to reach maximum height
--------------------------------------------
Here's the plot:
+graph%28+400%2C+400%2C+-2%2C+6%2C+-10%2C+30%2C+-4.9x%5E2+%2B+16x+%2B+14+%29+
check:
+h%5Bmax%5D+=+-4.9%2A1.633%5E2+%2B+16%2A1.633+%2B+14+
+h%5Bmax%5D+=+-13.067+%2B+26.128+%2B+14++
+h%5Bmax%5D+=+27.061+ m
This looks close on plot
OK

Answer by ikleyn(52847) About Me  (Show Source):
You can put this solution on YOUR website!
.

It is about finding the value of time "t", which maximize the given quadratic function.


For any quadratic function   y(x) = ax^2 + bx + c   with the negative leading coefficient "a", 

the value of the variable x, which provides the maximum to y(x), is  x= -b%2F%282a%29.


In your case,  a = -4.9, b = 16,  so the value of time "t" is


    t = -16%2F%282%2A%28-4.9%29%29 = 16%2F%282%2A4.9%29 = 1.633 seconds.    ANSWER

Solved, answered, calculated, explained and completed.

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My other lessons in this site on finding the maximum/minimum of a quadratic function are
    - HOW TO complete the square to find the minimum/maximum of a quadratic function
    - Briefly on finding the minimum/maximum of a quadratic function
    - HOW TO complete the square to find the vertex of a parabola
    - Briefly on finding the vertex of a parabola

Also,  you have this free of charge online textbook in ALGEBRA-I in this site
    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this textbook under the topic "Finding minimum/maximum of quadratic functions".


Save the link to this online textbook together with its description

Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson

to your archive and use it when it is needed.